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Nuclear weapons
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Nuclear weapons delivery is the technology and systems used to place a nuclear weapon at the position of detonation, on or near its target. Several methods have been developed to carry out this task.

Strategic nuclear weapons are used primarily as part of a doctrine of deterrence by threatening large targets, such as cities. Weapons meant for use in limited military maneuvers, such as destroying specific military, communications, or infrastructure targets, are known as tactical nuclear weapons. In terms of explosive yields, nowadays the former have much larger yield than the latter, even though it's not a rule. The bombs that destroyed Hiroshima and Nagasaki in 1945 (with TNT equivalents between 15 and 22 kilotons) were weaker than many of today's tactical weapons, yet they achieved the desired effect when used strategically.

Main delivery mechanisms[link]

[edit] Gravity bomb

The second nuclear weapons, such as the "Little Boy" and the "Fat Man" devices, were large and cumbersome gravity bombs

Historically, the first method of delivery, and the method used in the only two nuclear weapons actually used in warfare, was in a gravity bomb dropped by a bomber. In the years leading up to the development and deployment of nuclear-armed missiles, nuclear bombs represented the most practical means of nuclear weapons delivery; even today, and especially with the decommissioning of nuclear missiles, aerial bombing remains the primary means of offensive nuclear weapons delivery, and the majority of U.S. nuclear warheads are represented in bombs.

No nuclear weapon qualifies as a "wooden bomb"—US military slang for a bomb that is trouble-free, maintenance-free, and danger-free under all conditions. Gravity bombs are designed to be dropped from planes, which requires that the weapon can withstand vibrations and changes in air temperature and pressure during the course of a flight. Early weapons often had a removable core for safety, installed by the air crew during flight. They had to meet safety conditions, to prevent accidental detonation or dropping. A variety of types also had to have a fuse to initiate detonation. US nuclear weapons that met these criteria are designated by the letter "B" followed, without a hyphen, by the sequential number of the "physics package" it contains. The "B61", for example, was the primary bomb in the US arsenal for decades.

Various air-dropping techniques exist, including toss bombing, parachute-retarded delivery, and laydown modes, intended to give the dropping aircraft time to escape the ensuing blast.

The early gravity nuclear bombs could only be carried by the B-29 Superfortress. The next generation of weapons were still so big and heavy that they could only be carried by bombers such as the B-52 Stratofortress and V bombers, but by the mid-1950s smaller weapons had been developed that could be carried and deployed by fighter-bombers.

Ballistic missile[link]

Trident II SLBM launched by Royal Navy Vanguard class submarine.

Missiles using a ballistic trajectory usually deliver a warhead over the horizon, at distances of hundreds up to thousands of kilometers, as in the case of intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs). Most ballistic missiles exit the Earth's atmosphere and re-enter it in their sub-orbital spaceflight.

Placement of nuclear missiles on the low Earth orbit, a truly fearsome option, has been banned by Outer Space Treaty as early as 1967. Also, the eventual Soviet Fractional Orbital Bombardment System (FOBS) that served a similar purpose—it was just deliberately designed to deorbit before completing a full circle—was phased out in January 1983 in compliance with the SALT II treaty.

An ICBM is more than 20 times as fast as a bomber and more than 10 times as fast as a fighter plane, and also flying at a much higher altitude, and therefore more difficult to defend against. ICBMs can also be fired quickly in the event of a surprise attack.

Early ballistic missiles carried a single warhead, often of megaton-range yield. Because of the limited accuracy of the missiles, this kind of high yield was considered necessary in order to ensure a particular target's destruction. Since the 1970s modern ballistic weapons have seen the development of far more accurate targeting technologies, particularly due to improvements in inertial guidance systems. This set the stage for smaller warheads in the hundreds-of-kilotons-range yield, and consequently for ICBMs having multiple independently targetable reentry vehicles (MIRV). A single missile would now be used to launch an entire "bus", releasing up to a dozen independent warheads into a dozen different ballistic trajectories. MIRV has a number of advantages over a missile with a single warhead. With small additional costs, it allows a single missile to strike multiple targets, or to inflict maximum damage on a single target by attacking it with multiple warheads. It makes anti-ballistic missile defense even more difficult, and even less economically viable, than before.

Missile warheads in the American arsenal are indicated by the letter "W"; for example, the W61 missile warhead would have the same physics package as the B61 gravity bomb described above, but it would have different environmental requirements, and different safety requirements since it would not be crew-tended after launch and remain atop a missile for a great length of time.

Cruise missile[link]

Cruise missiles have a shorter range than ICBMs. BGM-109 Tomahawk pictured.

A cruise missile is a jet engine or rocket-propelled missile that flies at low altitude using an automated guidance system (usually inertial navigation, sometimes supplemented by either GPS or mid-course updates from friendly forces) to make them harder to detect or intercept. Cruise missiles can carry a nuclear warhead. They have a shorter range and smaller payloads than ballistic missiles, so their warheads are smaller and less powerful.

Unlike conventional cruise missiles, which sometimes use cluster munition payloads, and unlike bombers, nuclear armed cruise missiles have a single warhead.

The AGM-129 ACM (Advanced Cruise Missile) is the US Air Force's current nuclear-armed air-launched cruise missile. The START II treaty forbids the USA from using stealth weapons on stealth aircraft, therefore the ACM is only carried on the B-52 Stratofortress. This plane can carry 20 missiles. Thus the cruise missiles themselves can be compared with MIRV warheads. The BGM/UGM-109 Tomahawk sea-launched cruise missile is capable of carrying nuclear warheads, but does not in present configurations.

Cruise missiles may also be launched from mobile launchers on the ground, and from naval ships.

There is no letter change in the US arsenal to distinguish the warheads of cruise missiles from those for ballistic missiles.

Cruise missiles, even with their lower payload, have a number of advantages over ballistic missiles for the purposes of delivering nuclear strikes:

• Launch of a cruise missile is difficult to detect early from satellites and other long-range means, contributing to a surprise factor of attack.
• That, coupled with the ability to actively maneuver in flight, allows for penetration of strategic anti-missile systems aimed at intercepting ballistic missiles on calculated trajectory of flight.

Partially for those reasons, nuclear-armed cruise missiles are amongst the least deployed of all nuclear weapons, as their deployment is restricted by treaties such as SALT II.

Other delivery systems[link]

The Davy Crockett artillery shell is the smallest known nuclear weapon developed by the USA.

The Mk-17 was an early U.S. thermonuclear weapon and weighed around 21 short tons (19,000 kg).

Other potential delivery methods include artillery shells, mines such as the Medium Atomic Demolition Munition and the (very odd) Blue Peacock, and nuclear depth charges, and nuclear torpedoes. An atomic mortar was also tested. Even an 'Atomic Bazooka' was designed to be used against large formations of tanks.

In the 1950s the U.S. developed small nuclear warheads for air defense use, such as the Nike Hercules. From the 1950s to the 1980s, the United States and Canada fielded a low-yield nuclear-tipped air-to-air rocket, the AIR-2 Genie. Further developments of this concept, some with much larger warheads, led to the early anti-ballistic missiles. United States' have taken nuclear air-defense weapons out of service. Russia continues to maintain the Soviet anti-ballistic missiles with nuclear warheads.^{[citation needed]}

Small, two-man portable tactical weapons (erroneously referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty to combine sufficient yield with portability limits their military utility.

See also[link]

• History of nuclear weapons
• List of nuclear weapons
• Mutual assured destruction doctrine
• National missile defense of the United States
• Nuclear explosion
• Nuclear strategy
• Nuclear weapon design
• Nuclear terrorism

Notes[link]

References[link]

• Annotated bibliography for nuclear weapon delivery systems from the Alsos Digital Library for Nuclear Issues

External links[link]

Wikimedia Commons has media related to: Nuclear delivery

• Nuclear Missile Research Centre

Korean War 한국전쟁(韓國戰爭) 조선전쟁(朝鮮戰爭) Part of the Cold War Clockwise from top: U.S. Marines retreating during the Battle of Chosin Reservoir; U.N. landing at Incheon harbor, starting point of the Battle of Inchon; Korean refugees in front of an American M26 Pershing tank; U.S. Marines, led by First Lieutenant Baldomero Lopez, landing at Incheon; F-86 Sabre fighter aircraft. Date Full-scale: 25 June 1950 – 27 July 1953 (&100000000000000030000003 years, &1000000000000003200000032 days) Low-level: 27 July 1953 – present (&1000000000000005800000058 years, &10000000000000335000000335 days) Location Korean Peninsula Status Cease-fire armistice North Korean invasion of South Korea repelled U.N. invasion of North Korea repelled Chinese invasion of South Korea repelled Korean Demilitarized Zone established, little territorial change at the 38th parallel border, essentially uti possidetis Territorial changes Korean Demilitarized Zone established; both sides gained little border territory at the 38th parallel Belligerents  Republic of Korea  United Nations  United States of America  United Kingdom (U.N. Resolution 84) Combat support Australia  Belgium Canada  Colombia Ethiopian Empire  France Kingdom of Greece  Luxembourg Netherlands  New Zealand Philippines South Africa  Thailand  Turkey Medical support  Denmark  India  Italy  Norway  Sweden  Democratic People's Republic of Korea  People's Republic of China 22x20px Union of Soviet Socialist Republics Medical support People's Republic of Bulgaria Czechoslovak Socialist Republic[1] People's Republic of Hungary People's Republic of Poland Romanian People's Republic Other support People's Republic of Mongolia Commanders and leaders Rhee Syngman Chung Il-kwon Paik Sun-yup Shin Sung-mo Son Won-il Douglas MacArthur (Commander of the UNC) Matthew Ridgway (Commander of the UNC) Mark Wayne Clark (Commander of the UNC) Current Lee Myung-bak Kim Kwan-jin Jeong Seung-jo Kim Sang-ki Choi Yoon-hee Park Jong-heon James D. Thurman Kim Il-sung Pak Hon-yong Choi Yong-kun Kim Chaek Mao Zedong Peng Dehuai 22x20px Joseph Stalin Current Kim Jong-un Jang Sung-taek Kim Yong-Chun Ri Yong-ho Strength 600,000 302,000[2] 14,200[2] 6,150[2] 5,460[2] 3,972[3] 2,280[2] 1,500[2] 1,390[2] 1,290[2] 1,270[2] 1,260[2] 1,120[2] 1,070[2] 900[2] 300[2] 170[2] 105[2] 100[2] 72[2] 70[2] 44[2] Total: 941,600 Current 653,000 28,500 Total: 681,500 260,000 1,350,000[4] 22x20px 26,000 Total: 1,636,000 Note: The figures vary by source; peak unit strength varied during war. Current 1,106,000 Casualties and losses  Republic of Korea:[2] 137,899 dead 450,742 wounded 24,495 MIA 8,343 POW  United States of America: (US sources):[2] 36,940 dead 92,134 wounded 3,737 MIA 4,439 POW (PRC-DPRK estimates): 397,543 in total[5]  United Kingdom:[2] 1,078 dead 2,674 wounded 179 MIA 977 POW  Turkey:[2] 741 dead 2,068 wounded 163 MIA 244 POW Commonwealth of Australia: [6] 339 dead 1,216 wounded 43 MIA 26 POW Dominion of Canada:[2] 312 dead 1,212 wounded 1 MIA 32 POW  France:[2] 262 dead 1,008 wounded 7 MIA 12 POW Kingdom of Greece[2] 192 dead 543 wounded 3 POW  Colombia:[2] 163 dead 448 wounded 28 POW  Thailand:[2] 129 dead 1,139 wounded 5 MIA Ethiopian Empire[2] 121 dead 536 wounded Netherlands:[2] 120 dead 645 wounded Philippines:[2] 112 dead 229 wounded 16 MIA 41 POW  Belgium:[2] 99 dead 336 Wounded 4 MIA 1 POW Union of South Africa[2] 34 dead 9 POW  New Zealand:[2] 23 dead 79 wounded 1 MIA  Norway:[2] 3 dead  Luxembourg:[2] 2 dead 13 wounded Total: 776,360–1,093,839[5] Democratic People's Republic of Korea: 215,000 dead 303,000 wounded 120,000 MIA or POW[7] People's Republic of China: (Chinese sources):[8] 152,000 dead 383,500 wounded 450,000 hospitalized 4,000 missing 7,110 captured 14,190 defected (U.S. estimate):[7] 400,000+ dead 486,000 wounded 21,000 POW 22x20px Union of Soviet Socialist Republics: 282 dead[9] Total: 1,545,822–1,648,582 Total civilians killed/wounded: 2.5 million (est.)[2] South Korea: 990,968 373,599 killed[2] 229,625 wounded[2] 387,744 abducted/missing[2] North Korea: 1,550,000 (est.)[2]

v t e Korean War North Korean Offensive Operation Pokpoong Chuncheon Gorangpo Kaesong-Munsan Korea Strait Ongjin Uijeongbu Suwon Airfield Air Campaign Andong Chumonchin Chan Osan Pyongtaek Chonan Chochiwon Taejon Sangju Yongdong Hwanggan Hadong Notch Pusan Perimeter Masan P'ohang-Dong Taegu 1st Naktong Bulge Bowling Alley Battle Mountain Kyongju Haman Nam River Ka-San Tabu-Dong Yongsan 2nd Naktong Bulge United Nations Counteroffensive Haeju Inchon 2nd Seoul Hill 282 12 October 1950 Sariwon Yongju Kujin Chongju Chinese Intervention Onjong Unsan Pakchon Ch'ongch'on River Wawon Chosin Reservoir 3rd Seoul 1st and 2nd Wonju Operation Thunderbolt Twin Tunnels Hoengsong Chipyong-Ni 3rd Wonju Chuam-Ni Wonsan Operation Killer Operation Ripper Maehwa-San Operation Courageous Operation Tomahawk Operation Rugged Operation Dauntless 5th Seoul Imjin River Yultong Kapyong Soyang River Stalemate Bloody Ridge Heartbreak Ridge Han River Operation Commando 1st Maryang San 2nd Maryang San Sunchon Hill Eerie Sui-Ho Dam Old Baldy Operation Blaze White Horse Triangle Hill Pork Chop Hill Hook Outpost Harry Kumsong Samichon River Post Armistice D.M.Z. Conflict Blue House Raid EC-121 Incident Gangneung Border Incidents Yosu 1st Yeonpyeong 2nd Yeonpyeong Daecheong 3rd Yeonpyeong

The Korean War (Korean: 한국전쟁 or 조선전쟁, Hanja: 韓國戰爭 or 朝鮮戰爭; 25 June 1950 – 27 July 1953^[10][a]) was a war between the Republic of Korea (supported primarily by the United States of America, with contributions from allied nations under the aegis of the United Nations) and the Democratic People's Republic of Korea (supported by the People's Republic of China, with military and material aid from the Union of Soviet Socialist Republics). The Korean War was primarily the result of the political division of Korea by an agreement of the victorious Allies at the conclusion of the Pacific War at the end of World War II. The Korean Peninsula was ruled by the Empire of Japan from 1910 until the end of World War II. Following the surrender of the Empire of Japan in September 1945, American administrators divided the peninsula along the 38th parallel, with U.S. military forces occupying the southern half and Soviet military forces occupying the northern half.^[12]

The failure to hold free elections throughout the Korean Peninsula in 1948 deepened the division between the two sides; the North established a communist government, while the South established a capitalist one. The 38th parallel increasingly became a political border between the two Korean states. Although reunification negotiations continued in the months preceding the war, tension intensified. Cross-border skirmishes and raids at the 38th Parallel persisted. The situation escalated into open warfare when North Korean forces invaded South Korea on 25 June 1950.^[13] It was the first significant armed conflict of the Cold War.^[14] In 1950 the Soviet Union boycotted the United Nations security council, in protest at representation of China by the Kuomintang / Republic of China government, which had taken refuge in Taiwan following defeat in the Chinese Civil War. In the absence of a dissenting voice from the Soviet Union, who could have vetoed it, the United States and other countries passed a security council resolution authorizing military intervention in Korea.

The United States of America provided 88% of the 341,000 international soldiers which aided South Korean forces in repelling the invasion, with twenty other countries of the United Nations offering assistance. Suffering severe casualties, within two months the defenders were pushed back to a small area in the south of the Korean Peninsula, known as the Pusan perimeter. A rapid U.N. counter-offensive then drove the North Koreans past the 38th Parallel and almost to the Yalu River, when the People's Republic of China (PRC) entered the war on the side of North Korea.^[13] Chinese intervention forced the Southern-allied forces to retreat behind the 38th Parallel. While not directly committing forces to the conflict, the Soviet Union provided material aid to both the North Korean and Chinese armies. The active stage of the war ended on 27 July 1953, when the armistice agreement was signed. The agreement restored the border between the Koreas near the 38th Parallel and created the Korean Demilitarized Zone (DMZ), a 2.5-mile (4.0 km)-wide fortified buffer zone between the two Korean nations. Minor outbreaks of fighting continue to the present day.

With both North Korea and South Korea sponsored by external powers, the Korean War was a proxy war. From a military science perspective, it combined strategies and tactics of World War I and World War II: it began with a mobile campaign of swift infantry attacks followed by air bombing raids, but became a static trench war by July 1951.

Background[link]

Terminology[link]

In the United States of America, the war was initially described by President Harry S. Truman as a "police action" as it was conducted under the auspices of the United Nations.^[15] Colloquially, it has been referred to in the United States as The Forgotten War or The Unknown War because the issues concerned were much less clear than in previous and subsequent conflicts, such as World War II and the Vietnam War.^[16][17]

In South Korea the war is usually referred to as "625" or the 6–2–5 Upheaval (yug-i-o dongnan), reflecting the date of its commencement on 25 June.^[18] In North Korea the war is officially referred to as the Fatherland Liberation War (Choguk haebang chǒnjaeng). Alternatively, it is called the "Chosǒn War" (Chosǒn chǒnjaeng).^[19] In the People's Republic of China the war is officially called the War to Resist U.S. Aggression and Aid Korea (simplified Chinese: 抗美援朝战争; traditional Chinese: 抗美援朝戰爭; pinyin: Kàngměiyuáncháo zhànzhēng),^[20][21] although the term "Joseon War" (simplified Chinese: 朝鲜战争; traditional Chinese: 朝鮮戰爭; pinyin: Cháoxiǎn zhànzhēng) is also used in unofficial capacity.

Japanese rule (1910–1945)[link]

Upon defeating the Qing Dynasty in the First Sino-Japanese War (1894–96), the Empire of Japan occupied the Korean Empire – a peninsula strategic to its sphere of influence.^[22] A decade later, defeating Imperial Russia in the Russo-Japanese War (1904–05), Japan made Korea its protectorate with the Eulsa Treaty in 1905, then annexed it with the Japan–Korea Annexation Treaty in 1910.^[23]

Korean nationalists and the intelligentsia fled the country, and some founded the Provisional Korean Government in 1919, which was headed by Syngman Rhee in Shanghai. This government-in-exile was recognized by few countries. From 1919 to 1925 and beyond, Korean communists led and were the primary agents of internal and external warfare against the Japanese.^[24][25]

Korea under Japanese rule was considered to be part of the Empire of Japan as an industrialized colony along with Taiwan, and both were part of the Greater East Asia Co-Prosperity Sphere. In 1937, the colonial Governor-General, General Jirō Minami, commanded the attempted cultural assimilation of Korea's 23.5 million people by banning the use and study of Korean language, literature, and culture, to be replaced with that of mandatory use and study of their Japanese counterparts. Starting in 1939, the populace was required to use Japanese names under the Sōshi-kaimei policy. In 1938, the Colonial Government established labor conscription.^{[citation needed]}

In the People's Republic of China, the National Revolutionary Army and the Communist People's Liberation Army helped organize refugee Korean patriots and independence fighters against the Japanese military, which had also occupied parts of China. The Nationalist-backed Koreans, led by Yi Pom-Sok, fought in the Burma Campaign (December 1941 – August 1945). The Communists, led by Kim Il-sung, fought the Japanese in Korea and Manchuria.^{[citation needed]}

During World War II, the Japanese used Korea's food, livestock, and metals for their war effort. Japanese forces in Korea increased from 46,000 soldiers in 1941 to 300,000 in 1945. Japanese Korea conscripted 2.6 million forced laborers controlled with a collaborationist Korean police force; some 723,000 people were sent to work in the overseas empire and in metropolitan Japan. By 1942, Korean men were being conscripted into the Imperial Japanese Army. By January 1945, Koreans comprised 32% of Japan's labor force. In August 1945, when the United States dropped atomic bombs on Hiroshima and Nagasaki, around 25% of those killed were Koreans.^[25] At the end of the war, other world powers did not recognize Japanese rule in Korea and Taiwan.

Meanwhile, at the Cairo Conference (November 1943), Nationalist China, the United Kingdom, and the United States decided "in due course Korea shall become free and independent".^[26] Later, the Yalta Conference (February 1945) granted to the Soviet Union European "buffer zones"—satellite states accountable to Moscow—as well as an expected Soviet pre-eminence in China and Manchuria, in return for joining the Allied Pacific War effort against Japan.^[27]

Soviet invasion of Manchuria (1945)[link]

Toward the end of World War II, as per a US-Soviet agreement, the Soviet Union declared war against Japan on 9 August 1945.^[25][28] By 10 August, the Red Army occupied the northern part of the Korean peninsula as agreed, and on 26 August halted at the 38th parallel for three weeks to await the arrival of US forces in the south.^[29]

On 10 August 1945, with the 15 August Japanese surrender near, the Americans doubted whether the Soviets would honor their part of the Joint Commission, the US-sponsored Korean occupation agreement. A month earlier, Colonel Dean Rusk and Colonel Charles H. Bonesteel III divided the Korean peninsula at the 38th parallel after hurriedly deciding that the US Korean Zone of Occupation had to have a minimum of two ports.^{[30][31][32][33]}

Explaining why the occupation zone demarcation was positioned at the 38th parallel, Rusk observed, "even though it was further north than could be realistically reached by US forces, in the event of Soviet disagreement ... we felt it important to include the capital of Korea in the area of responsibility of American troops", especially when "faced with the scarcity of US forces immediately available, and time and space factors, which would make it difficult to reach very far north, before Soviet troops could enter the area."^[27] The Soviets agreed to the US occupation zone demarcation to improve their negotiating position regarding the occupation zones in Eastern Europe, and because each would accept Japanese surrender where they stood.^[34]

Chinese Civil War (1945–1949)[link]

After the end of Second Sino-Japanese War, the Chinese Civil War resumed between the Chinese Communists and the Chinese Nationalists. While the Communists were struggling for supremacy in Manchuria, they were supported by the North Korean government with materiel and manpower.^[35] According to Chinese sources, the North Koreans donated 2,000 railway cars worth of material while thousands of Korean "volunteers" served in the Chinese People's Liberation Army (PLA) during the war.^[36] North Korea also provided the Chinese Communists in Manchuria with a safe refuge for non-combatants and communications with the rest of China.^[35]

The North Korean contributions to the Chinese Communist victory were not forgotten after the creation of the People's Republic of China in 1949. As a token of gratitude, between 50,000 to 70,000 Korean veterans that served in the PLA were sent back along with their weapons, and they would later play a significant role in the initial invasion of South Korea.^[35] China promised to support the North Koreans in the event of a war against South Korea.^[37] The Chinese support created a deep division between the Korean Communists, and Kim Il-Sung's authority within the Communist party was challenged by the Chinese faction led by Pak Il-yu, who was later purged by Kim.^[38]

After the formation of the People's Republic of China in 1949, the Chinese government named the Western nations, led by the United States, as the biggest threat to its national security.^[39] Basing this judgment on China's century of humiliation beginning in the early 19th century,^[40] American support for the Nationalists during the Chinese Civil War,^[41] and the ideological struggles between revolutionaries and reactionaries,^[42] the Chinese leadership believed that China would become a critical battleground in the United States' crusade against Communism.^[43] As a countermeasure and to elevate China's standing among the worldwide Communist movements, the Chinese leadership adopted a foreign policy that actively promoted Communist revolutions throughout territories on China's periphery.^[44]

Korea divided (1945–1949)[link]

At the Potsdam Conference (July–August 1945), the Allies unilaterally decided to divide Korea—without consulting the Koreans—in contradiction of the Cairo Conference.^{[45][46][47][48]}

On 8 September 1945, Lt. Gen. John R. Hodge of the United States arrived in Incheon to accept the Japanese surrender south of the 38th parallel.^[31] Appointed as military governor, General Hodge directly controlled South Korea via the United States Army Military Government in Korea (USAMGIK 1945–48).^[49] He established control by restoring to power the key Japanese colonial administrators and their Korean police collaborators.^[14] The USAMGIK refused to recognise the provisional government of the short-lived People's Republic of Korea (PRK) because he suspected it was communist. These policies, voiding popular Korean sovereignty, provoked civil insurrections and guerrilla warfare.^[23] On 3 September 1945, Lieutenant General Yoshio Kozuki, Commander, Japanese Seventeenth Area Army, contacted Hodge, telling him that the Soviets were south of the 38th parallel at Kaesong. Hodge trusted the accuracy of the Japanese Army report^[31]

In December 1945, Korea was administered by a United States–Soviet Union Joint Commission, as agreed at the Moscow Conference (1945). The Koreans were excluded from the talks. The commission decided the country would become independent after a five-year trusteeship action facilitated by each régime sharing its sponsor's ideology.^[50][51] The Korean populace revolted; in the south, some protested, and some rose in arms;^[23] to contain them, the USAMGIK banned strikes on 8 December 1945 and outlawed the PRK Revolutionary Government and the PRK People's Committees on 12 December 1945.

On 23 September 1946 an 8,000-strong railroad worker strike began in Pusan. Civil disorder spread throughout the country in what became known as the Autumn uprising. On 1 October 1946, Korean police killed three students in the Daegu Uprising; protesters counter-attacked, killing 38 policemen. On 3 October, some 10,000 people attacked the Yeongcheon police station, killing three policemen and injuring some 40 more; elsewhere, some 20 landlords and pro-Japanese South Korean officials were killed.^[52] The USAMGIK declared martial law.

The right-wing Representative Democratic Council, led by nationalist Syngman Rhee, opposed the Soviet–American trusteeship of Korea, arguing that after 35 years (1910–45) of Japanese colonial rule most Koreans opposed another foreign occupation. The USAMGIK decided to forego the five year trusteeship agreed upon in Moscow, given the 31 March 1948 United Nations election deadline to achieve an anti-communist civil government in the US Korean Zone of Occupation.

On 3 April what began as a demonstration commemorating Korean resistance to Japanese rule ended with the Jeju massacre of as many as 60,000 citizens by South Korean soldiers.^[53]

On 10 May, South Korea convoked their first national general elections that the Soviets first opposed, then boycotted, insisting that the US honor the trusteeship agreed to at the Moscow Conference.^[54][55]

North Korea held parliamentary elections three months later on 25 August 1948.^[56]

The resultant anti-communist South Korean government promulgated a national political constitution on 17 July 1948, elected a president, the American-educated strongman Syngman Rhee on 20 July 1948. The elections were marred by terrorism and sabotage resulting in 600 deaths.^[57] The Republic of Korea (South Korea) was established on 15 August 1948. In the Russian Korean Zone of Occupation, the Soviet Union established a Communist North Korean government^[54] led by Kim Il-sung.^[58] President Rhee's régime expelled communists and leftists from southern national politics. Disenfranchised, they headed for the hills, to prepare for guerrilla war against the US-sponsored ROK Government.^[58]

As nationalists, both Syngman Rhee and Kim Il-Sung were intent upon reunifying Korea under their own political system.^[59] With Joseph Stalin and Mao Zedong fighting over the control of the Korean Peninsula,^[60] the North Koreans gained support from both the Soviet Union and the People's Republic of China. They escalated the continual border skirmishes and raids and then prepared to invade. South Korea, with limited matériel, could not match them.^[59] During this era, at the beginning of the Cold War, the US government assumed that all communists, regardless of nationality, were controlled or directly influenced by Moscow; thus the US portrayed the civil war in Korea as a Soviet hegemonic maneuver.^[61]

In October 1948, South Korean left-wing soldiers rebelled against the government's harsh clampdown in April on Jeju island in the Yeosu-Suncheon Rebellion.^[62]

The Soviet Union withdrew as agreed from Korea in 1948. U.S. troops withdrew from Korea in 1949, leaving the South Korean army relatively ill-equipped. On 24 December 1949, South Korean forces killed 86 to 88 people in the Mungyeong massacre and blamed the crime on communist marauding bands.^[63][64]

Course of the war[link]

The conflict begins (June 1950)[link]

Territory often changed hands early in the war, until the front stabilized.

In April 1950 Kim Il-sung travelled to Moscow and secured Stalin's support for a policy to unify Korea under his authority. Although agreeing with the invasion of South Korea in principle, Stalin refused to become directly involved in Kim's plans, and advised Kim to enlist Chinese support instead. In May 1950 Kim visited Beijing, and succeeded in gaining Mao's endorsement. At the time, Mao's support for Kim was largely political (he was contemplating the invasions of Taiwan and Tibet), and was unaware of Kim's precise intentions or the timing of Kim's attack. When the Korean war broke out, the Chinese were in the process of demobilizing half of the PLA's 5.6 million soldiers.^[65]

On 7 June 1950, Kim Il-sung called for an election in whole Korea on 5–8 August 1950 and a consultative conference in Haeju on 15–17 June 1950. On June 11, the North sent three diplomats to the South, who were later arrested by the South. Fourteen days later on 25 June 1950, the North Korean People's Army (KPA) crossed the 38th parallel border and invaded South Korea.

Under the guise of counter-attacking a South Korean provocation raid, the KPA crossed the 38th parallel behind artillery fire at dawn on Sunday 25 June 1950.^[66] The KPA said that Republic of Korea Army (ROK Army) troops, under command of the régime of the "bandit traitor Syngman Rhee", had crossed the border first, and that they would arrest and execute Rhee.^[31] Both Korean armies had continually harassed each other with skirmishes and each continually staged raids across the 38th parallel border.

On 27 June, Rhee evacuated from Seoul with government officials. Rhee ordered the Bodo League massacre, which started on 28 June.^[67][68][69]

On 28 June, South Korea bombed the bridge across the Han River to stop the North Korean army.^[70]

Early on in the fighting, South Korea put its forces under the authority of the United Nations Command (Korea).^[71]

Factors in U.S. intervention[link]

The Truman Administration was caught at a crossroads. Before the invasion, Korea was not included in the strategic Asian Defense Perimeter outlined by Secretary of State Acheson.^[72] Military strategists were more concerned with the security of Europe against the Soviet Union than East Asia. At the same time, the Administration was worried that a war in Korea could quickly widen into another world war should the Chinese or Soviets decide to get involved as well.

One facet of the changing attitude toward Korea and whether to get involved was Japan. Especially after the fall of China to the Communists, "...Japan itself increasingly appeared as the major East Asian prize to be protected". U.S. East Asian experts saw Japan as the critical counterweight to the Soviet Union and China in the region. While there was no United States policy that dealt with South Korea directly as a national interest, its proximity to Japan pushed South Korea to the fore. "The recognition that the security of Japan required a non-hostile Korea led directly to President Truman's decision to intervene... The essential point... is that the American response to the North Korean attack stemmed from considerations of US policy toward Japan."^[73] The United States wanted to shore up Japan to make it a viable counterweight against the Soviet Union and China, and Korea was seen as integral to that end.

Hundreds of thousands of South Koreans fled south in mid-1950 after the North Korean army invaded.

The other important part of committing to intervention lay in speculation about Soviet action in the event that the United States intervene. The Truman administration was fretful that a war in Korea was a diversionary assault that would escalate to a general war in Europe once the US committed in Korea. At the same time, "[t]here was no suggestion from anyone that the United Nations or the United States could back away from [the conflict]".^[74] In Truman's mind, this aggression, if left unchecked, would start a chain reaction that would destroy the United Nations and give the go ahead to further Communist aggression elsewhere. Korea was where a stand had to be made, the difficult part was how. The UN Security council approved the use of force to help the South Koreans and the US immediately began using air and naval forces in the area to that end. The Administration still refrained from committing on the ground because some advisors believed the North Koreans could be stopped by air and naval power alone.^[75]

Also, it was still uncertain if this was a clever ploy by the Soviet Union to catch the US unawares or just a test of US resolve. The decision to commit ground troops and to intervene eventually became viable when a communiqué was received on 27 June from the Soviet Union that alluded it would not move against US forces in Korea. "This opened the way for the sending of American ground forces, for it now seemed less likely that a general war—with Korea as a preliminary diversion—was imminent".^[76] With the Soviet Union's tacit agreement that this would not cause an escalation, the United States now could intervene with confidence that other commitments would not be jeopardized.

United Nations Security Council Resolutions[link]

On 25 June 1950, the United Nations Security Council unanimously condemned the North Korean invasion of the Republic of Korea, with United Nations Security Council Resolution 82. The Soviet Union, a veto-wielding power, had boycotted the Council meetings since January 1950, protesting that the Republic of China (Taiwan), not the People's Republic of China, held a permanent seat in the UN Security Council.^[77] After debating the matter, the Security Council, on 27 June 1950, published Resolution 83 recommending member states provide military assistance to the Republic of Korea. On 27 June President Truman ordered US air and sea forces to help the South Korean régime. On 4 July the Soviet Deputy Foreign Minister accused the US of starting armed intervention on behalf of South Korea.^[78]

The Soviet Union challenged the legitimacy of the war for several reasons. The ROK Army intelligence upon which Resolution 83 was based came from US Intelligence; North Korea was not invited as a sitting temporary member of the UN, which violated UN Charter Article 32; and the Korean conflict was beyond UN Charter scope, because the initial north–south border fighting was classed as a civil war. The Soviet representative boycotted the UN to prevent Security Council action, and to challenge the legitimacy of the UN action; legal scholars posited that deciding upon an action of this type required the unanimous vote of the five permanent members.^[79][80]

Comparison of military forces[link]

In early 1951 USAF recruits arrived by the train load, more than doubling the population of Lackland AFB.

By mid-1950 North Korean forces numbered between 150,000 and 200,000 troops, organized into 10 infantry divisions, one tank division, and one air force division, with 210 fighter planes and 280 tanks who captured scheduled objectives and territory, among them Kaesong, Chuncheon, Uijeongbu, and Ongjin. Their forces included 274 T-34-85 tanks, some 150 Yak fighters, 110 attack bombers, 200 artillery pieces, 78 Yak trainers, and 35 reconnaissance aircraft.^[31] In addition to the invasion force, the North Korean KPA had 114 fighters, 78 bombers, 105 T-34-85 tanks, and some 30,000 soldiers stationed in reserve in North Korea.^[31] Although each navy consisted of only several small warships, the North Korean and South Korean navies fought in the war as sea-borne artillery for their in-country armies.

In contrast, the ROK Army defenders were vastly unprepared, and the political establishment in the south, while well aware of the threat to the north, were unable to convince American administrators of the reality of the threat. In South to the Naktong, North to the Yalu (1961), R.E. Appleman reports the ROK forces' low combat readiness as of 25 June 1950. The ROK Army had 98,000 soldiers (65,000 combat, 33,000 support), no tanks (they had been requested from the US military, but requests were denied), and a 22–piece air force comprising 12 liaison-type and 10 AT6 advanced-trainer airplanes. There were no large foreign military garrisons in Korea at invasion time, but there were large US garrisons and air forces in Japan.^[31]

Within days of the invasion, masses of ROK Army soldiers—of dubious loyalty to the Syngman Rhee régime—were either retreating southwards or were defecting en masse to the northern side, the KPA.^[24]

United Nations response (July – August 1950)[link]

A US howitzer position near the Kum River, 15 July.

A GI comforts a grieving infantryman.

Despite the rapid post–Second World War Allied demobilizations, there were substantial US forces occupying Japan; under General Douglas MacArthur's command, they could be made ready to fight the North Koreans.^[81] Only the British Commonwealth had comparable forces in the area.

On Saturday, 24 June 1950, US Secretary of State Dean Acheson informed President Truman by telephone, "Mr. President, I have very serious news. The North Koreans have invaded South Korea."^[82][83] Truman and Acheson discussed a US invasion response with defense department principals, who agreed that the United States was obligated to repel military aggression, paralleling it with Adolf Hitler's 1930s aggressions, and said that the mistake of appeasement must not be repeated.^[84] In his autobiography, President Truman acknowledged that fighting the invasion was essential to the American goal of the global containment of communism as outlined in the National Security Council Report 68 (NSC-68) (declassified in 1975):

Communism was acting in Korea, just as Hitler, Mussolini and the Japanese had ten, fifteen, and twenty years earlier. I felt certain that if South Korea was allowed to fall Communist leaders would be emboldened to override nations closer to our own shores. If the Communists were permitted to force their way into the Republic of Korea without opposition from the free world, no small nation would have the courage to resist threat and aggression by stronger Communist neighbors.^[85]

President Truman announced that the US would counter "unprovoked aggression" and "vigorously support the effort of the [UN] security council to terminate this serious breach of peace."^[83] In Congress, the Joint Chiefs of Staff Chairman General Omar Bradley warned against appeasement, saying that Korea was the place "for drawing the line" against communist expansion. In August 1950, the President and the Secretary of State obtained the consent of Congress to appropriate $12 billion to pay for the military expenses.^[83]

Per State Secretary Acheson's recommendation, President Truman ordered General MacArthur to transfer materiel to the Army of the Republic of Korea while giving air cover to the evacuation of US nationals. The President disagreed with advisors who recommended unilateral US bombing of the North Korean forces, and ordered the US Seventh Fleet to protect the Republic of China (Taiwan), whose Nationalist Government asked to fight in Korea. The US denied the Nationalist Chinese request for combat, lest it provoke a communist Chinese retaliation.^[86] Because the US had sent the Seventh Fleet to "neutralize" the Taiwan Strait, Chinese premier Zhou Enlai criticized both the UN and US initiatives as "armed aggression on Chinese territory."^[87]

The Battle of Osan, the first significant American engagement of the Korean War, involved the 540-soldier Task Force Smith, which was a small forward element of the 24th Infantry Division.^[88] On 5 July 1950, Task Force Smith attacked the North Koreans at Osan but without weapons capable of destroying the North Koreans' tanks. They were unsuccessful; the result was 180 dead, wounded, or taken prisoner. The KPA progressed southwards, pushing back the US force at Pyongtaek, Chonan, and Chochiwon, forcing the 24th Division's retreat to Taejeon, which the KPA captured in the Battle of Taejon;^[89] the 24th Division suffered 3,602 dead and wounded and 2,962 captured, including the Division's Commander, Major General William F. Dean.^[89] Overhead, the KPAF shot down 18 USAF fighters and 29 bombers; the USAF shot down five KPAF fighters.^{[citation needed]}

By August, the KPA had pushed back the ROK Army and the Eighth United States Army to the vicinity of Pusan, in southeast Korea.^[90] In their southward advance, the KPA purged the Republic of Korea's intelligentsia by killing civil servants and intellectuals.^[91] On 20 August, General MacArthur warned North Korean leader Kim Il-Sung that he was responsible for the KPA's atrocities.^[91] By September, the UN Command controlled the Pusan perimeter, enclosing about 10% of Korea, in a line partially defined by the Nakdong River.

Although Kim's early successes had led him to predict that he would end the war by the end of August, Chinese leaders were more pessimistic. To counter the possibility of American invasion, Zhou Enlai secured a Soviet commitment to have the Soviet Union support Chinese forces with air cover, and deployed 260,000 soldiers along the Korean border, under the command of Gao Gang. Zhou commanded Chai Chengwen to conduct a topographical survey of Korea, and directed Lei Yingfu, Zhou's military advisor in Korea, to analyze the military situation in Korea. Lei concluded that MacArthur would most likely attempt a landing at Incheon. After conferring with Mao that this would be MacArthur's most likely strategy, Zhou briefed Soviet and North Korean advisers of Lei's findings, and issued orders to Chinese army commanders deployed on the Korean border to prepare for American naval activity in the Korea Strait.^[92]

Escalation (August – September 1950)[link]

The U.S. Air Force attacking railroads south of Wonsan on the eastern coast of North Korea.

In the resulting Battle of Pusan Perimeter (August–September 1950), the US Army withstood KPA attacks meant to capture the city at the Naktong Bulge, P'ohang-dong, and Taegu. The United States Air Force (USAF) interrupted KPA logistics with 40 daily ground support sorties that destroyed 32 bridges, halting most daytime road and rail traffic. KPA forces were forced to hide in tunnels by day and move only at night.^[93]To deny materiel to the KPA, the USAF destroyed logistics depots, petroleum refineries, and harbors, while the US Navy air forces attacked transport hubs. Consequently, the over-extended KPA could not be supplied throughout the south.^[94]

Meanwhile, US garrisons in Japan continually dispatched soldiers and materiel to reinforce defenders in the Pusan Perimeter.^[95] Tank battalions deployed to Korea directly from the United States mainland from the port of San Francisco to the port of Pusan, the largest Korean port. By late August, the Pusan Perimeter had some 500 medium tanks battle ready.^[96] In early September 1950, ROK Army and UN Command forces outnumbered the KPA 180,000 to 100,000 soldiers. The UN forces, once prepared, counterattacked and broke out of the Pusan Perimeter.^[22][97]

Battle of Inchon (September 1950)[link]

General Douglas MacArthur, UN Command CiC (seated), observes the naval shelling of Incheon from the USS Mt. McKinley, 15 September 1950.

Against the rested and re-armed Pusan Perimeter defenders and their reinforcements, the KPA were undermanned and poorly supplied; unlike the UN Command, they lacked naval and air support.^[98] To relieve the Pusan Perimeter, General MacArthur recommended an amphibious landing at Inchon, well over 100 miles (160 km) behind the KPA lines.^[99] On 6 July, he ordered Major General Hobart R. Gay, Commander, 1st Cavalry Division, to plan the division's amphibious landing at Incheon; on 12–14 July, the 1st Cavalry Division embarked from Yokohama, Japan to reinforce the 24th Infantry Division inside the Pusan Perimeter.^[100]

Soon after the war began, General MacArthur had begun planning a landing at Incheon, but the Pentagon opposed him.^[99] When authorized, he activated a combined United States Army, United States Marine Corps, and ROK Army force. The X Corps, led by General Edward Almond, Commander, consisted of 40,000 men of the 1st Marine Division, the 7th Infantry Division and around 8,600 ROK Army soldiers.^[101] By the 15 September attack date, the amphibious assault force faced few KPA defenders at Incheon: military intelligence, psychological warfare, guerrilla reconnaissance, and protracted bombardment facilitated a relatively light battle. However, the bombardment destroyed most of the city of Incheon.^[102]

After the Incheon landing the 1st Cavalry Division began its northward advance from the Pusan Perimeter. "Task Force Lynch"—3rd Battalion, 7th Cavalry Regiment, and two 70th Tank Battalion units (Charlie Company and the Intelligence–Reconnaissance Platoon)— effected the "Pusan Perimeter Breakout" through 106.4 miles (171.2 km) of enemy territory to join the 7th Infantry Division at Osan.^[100] The X Corps rapidly defeated the KPA defenders around Seoul, thus threatening to trap the main KPA force in Southern Korea,^[103].

On 18 September Stalin dispatched General H.M. Zakharov to Korea to advise Kim Il-sung to halt his offensive around the Pusan perimeter and to redeploy his forces to defend Seoul. Chinese commanders were not briefed on North Korean troop numbers or operational plans. As the overall commander of Chinese forces, Zhou Enlai suggested that the North Koreans should attempt to eliminate the enemy forces at Inchon only if they had reserves of at least 100,000 men; otherwise, he advised the North Koreans to withdraw their forces north.^[104]

On 25 September Seoul was recaptured by South Korean forces. American air raids caused heavy damage to the KPA, destroying most of its tanks and much of its artillery. North Korean troops in the south, instead of effectively withdrawing north, rapidly disintegrated, leaving Pyongyang vulnerable.^[104] During the general retreat only 25,000 to 30,000 soldiers managed to rejoin the Northern KPA lines.^[105][106] On 27 September Stalin convened an emergency session of the Politburo, in which he condemned the incompetence of the KPA command and held Soviet military advisers responsible for the defeat.^[104]

UN forces cross partition line (September – October 1950)[link]

Combat in the streets of Seoul

On 27 September, MacArthur received the top secret National Security Council Memorandum 81/1 from Truman reminding him that operations north of the 38th parallel were authorized only if "at the time of such operation there was no entry into North Korea by major Soviet or Chinese Communist forces, no announcements of intended entry, nor a threat to counter our operations militarily..."^[107] On 29 September MacArthur restored the government of the Republic of Korea under Syngman Rhee.^[104] On 30 September, Defense Secretary George Marshall sent an eyes-only message to MacArthur: "We want you to feel unhampered tactically and strategically to proceed north of the 38th parallel."^[107] During October, the ROK police executed people who were suspected to be sympathetic to North Korea.^[108]

On 30 September Zhou Enlai warned the United States that it was prepared to intervene in Korea if the United States crossed the 38th parallel. Zhou attempted to advise North Korean commanders on how to conduct a general withdrawal by using the same tactics which had allowed Chinese communist forces to successfully escape Chiang Kai-shek's Encirclement Campaigns in the 1930s. North Korean commanders did not utilize these tactics effectively.^[109]

By 1 October 1950, the UN Command repelled the KPA northwards, past the 38th parallel; the ROK Army crossed after them, into North Korea.^[110] MacArthur made a statement demanding the KPA's unconditional surrender.^[111] Six days later, on 7 October, with UN authorization, the UN Command forces followed the ROK forces northwards.^[112] The X Corps landed at Wonsan (in southeastern North Korea) and Riwon (in northeastern North Korea), already captured by ROK forces.^[113] The Eighth United States Army and the ROK Army drove up western Korea and captured Pyongyang city, the North Korean capital, on 19 October 1950.^[114] The 187th Airborne Regimental Combat Team ("Rakkasans") made their first of two combat jumps during the Korean War on 20 October 1950 at Sunchon and Sukchon. The missions of the 187th were to cut the road north going to China, preventing North Korean leaders from escaping from Pyongyang; and to rescue American prisoners of war. At month's end, UN forces held 135,000 KPA prisoners of war.

Taking advantage of the UN Command's strategic momentum against the communists, General MacArthur believed it necessary to extend the Korean War into China to destroy depots supplying the North Korean war effort. President Truman disagreed, and ordered caution at the Sino-Korean border.^[115]

China intervenes (October – December 1950)[link]

On 27 June 1950, two days after the KPA invaded and three months before the Chinese entered the war, President Truman dispatched the United States Seventh Fleet to the Taiwan Strait, to prevent hostilities between the Nationalist Republic of China (Taiwan) and the People's Republic of China (PRC).^[116][117] On 4 August 1950, with the PRC invasion of Taiwan aborted, Mao Zedong reported to the Politburo that he would intervene in Korea when the People's Liberation Army's (PLA) Taiwan invasion force was reorganized into the PLA North East Frontier Force.

On 20 August 1950, Premier Zhou Enlai informed the United Nations that "Korea is China's neighbor... The Chinese people cannot but be concerned about a solution of the Korean question". Thus, via neutral-country diplomats, China warned that in safeguarding Chinese national security, they would intervene against the UN Command in Korea.^[115] President Truman interpreted the communication as "a bald attempt to blackmail the UN", and dismissed it.^[118]

Korean War flying aces,1950

1 October 1950, the day that UN troops crossed the 38th parallel, was also the first anniversary of the founding of the People's Republic of China. On that day the Soviet ambassador forwarded a telegram from Stalin to Mao and Zhou requesting that China send five to six divisions into Korea, and Kim Il-sung sent frantic appeals to Mao for Chinese military intervention. At the same time, Stalin made it clear that Soviet forces themselves would not directly intervene.^[111]

In a series of emergency meetings that lasted from 2–5 October, Chinese leaders debated whether to send Chinese troops into Korea. There was considerable resistance among many leaders, including senior military leaders, to confronting the United States in Korea. Mao strongly supported intervention, and Zhou was one of the few Chinese leaders who firmly supported him. After General Lin Biao refused Mao's offer to command Chinese forces in Korea (citing poor health), Mao called General Peng Dehuai to Beijing to hear his views. After listening to both sides' arguments, Peng supported Mao's position, and the Politburo agreed to intervene in Korea.^[119] Later, the Chinese claimed that US bombers had violated PRC national airspace while en route to bomb North Korea before China intervened.^[120] On 8 October 1950, Mao Zedong redesignated the PLA North East Frontier Force as the Chinese People's Volunteer Army (PVA).^[121]

In order to enlist Stalin's support, Zhou traveled to Stalin's summer resort on the Black Sea on 10 October. Stalin initially agreed to send military equipment and ammunition, but warned Zhou that the Soviet Union's air force would need two or three months to prepare any operations. In a subsequent meeting, Stalin told Zhou that he would only provide China with equipment on a credit basis, and that the Soviet air force would only operate over Chinese airspace, and only after an undisclosed period of time. Stalin did not agree to send either military equipment or air support until March 1951.^[122] Mao did not find Soviet air support especially useful, as the fighting was going to take place on the south side of the Yalu.^[123] Soviet shipments of materiel, when they did arrive, were limited to small quantities of trucks, grenades, machine guns, and the like.^[124]

Immediately on his return to Beijing on 18 October 1950, Zhou met with Mao Zedong, Peng Dehuai, and Gao Gang, and the group ordered two hundred thousand Chinese troops to enter North Korea, which they did on 25 October. After consulting with Stalin, on 13 November, Mao appointed Zhou the overall commander and coordinator of the war effort, with Peng as field commander. Orders given by Zhou were delivered in the name of the Central Military Commission.^[125]

New Zealand artillery crew in action

Soldiers from the U.S. 2nd Infantry Division in action near the Ch'ongch'on River, 20 November 1950

UN aerial reconnaissance had difficulty sighting PVA units in daytime, because their march and bivouac discipline minimized aerial detection.^[126] The PVA marched "dark-to-dark" (19:00–03:00), and aerial camouflage (concealing soldiers, pack animals, and equipment) was deployed by 05:30. Meanwhile, daylight advance parties scouted for the next bivouac site. During daylight activity or marching, soldiers were to remain motionless if an aircraft appeared, until it flew away;^[126] PVA officers were under order to shoot security violators. Such battlefield discipline allowed a three-division army to march the 286 miles (460 km) from An-tung, Manchuria to the combat zone in some 19 days. Another division night-marched a circuitous mountain route, averaging 18 miles (29 km) daily for 18 days.^[31]

Meanwhile, on 10 October 1950, the 89th Tank Battalion was attached to the 1st Cavalry Division, increasing the armor available for the Northern Offensive. On 15 October, after moderate KPA resistance, the 7th Cavalry Regiment and Charlie Company, 70th Tank Battalion captured Namchonjam city. On 17 October, they flanked rightwards, away from the principal road (to Pyongyang), to capture Hwangju. Two days later, the 1st Cavalry Division captured Pyongyang, the North's capital city, on 19 October 1950.

On 15 October 1950, President Truman and General MacArthur met at Wake Island in the mid-Pacific Ocean. This meeting was much publicized because of the General's discourteous refusal to meet the President on the continental US.^[127] To President Truman, MacArthur speculated there was little risk of Chinese intervention in Korea,^[128] and that the PRC's opportunity for aiding the KPA had lapsed. He believed the PRC had some 300,000 soldiers in Manchuria, and some 100,000–125,000 soldiers at the Yalu River. He further concluded that, although half of those forces might cross south, "if the Chinese tried to get down to Pyongyang, there would be the greatest slaughter" without air force protection.^[105][129]

After secretly crossing the Yalu River on 19 October, the PVA 13th Army Group launched the First Phase Offensive on 25 October, attacking the advancing UN forces near the Sino-Korean border. After decimating the ROK II Corps at the Battle of Onjong, the first confrontation between Chinese and US military occurred on 1 November 1950; deep in North Korea, thousands of soldiers from the PVA 39th Army encircled and attacked the US 8th Cavalry Regiment with three-prong assaults—from the north, northwest, and west—and overran the defensive position flanks in the Battle of Unsan.^[130] The surprise assault resulted in the UN forces retreating back to the Ch'ongch'on River, while the Chinese unexpectedly disappeared into mountain hideouts following victory. It is unclear why the Chinese did not press the attack and follow-up their victory.

The UN Command, however, were unconvinced that the Chinese had openly intervened due to the sudden Chinese withdrawal. On 24 November, the Home-by-Christmas Offensive was launched with the US Eighth Army advancing in northwest Korea, while the US X Corps were attacking along the Korean east coast. But the Chinese were waiting in ambush with their Second Phase Offensive.

On 25 November at the Korean western front, the PVA 13th Army Group attacked and over-ran the ROK II Corps at the Battle of the Ch'ongch'on River, and then decimated the US 2nd Infantry Division on the UN forces' right flank.^[131] The UN Command retreated; the US Eighth Army's retreat (the longest in US Army history)^[132] was made possible because of the Turkish Brigade's successful, but very costly, rear-guard delaying action near Kunuri that slowed the PVA attack for two days (27–9 November). On 27 November at the Korean eastern front, a US 7th Infantry Division Regimental Combat Team (3,000 soldiers) and the US 1st Marine Division (12,000–15,000 marines) were unprepared for the PVA 9th Army Group's three-pronged encirclement tactics at the Battle of Chosin Reservoir, but they managed to escape under Air Force and X Corps support fire—albeit with some 15,000 collective casualties.^[133]

By 30 November, the PVA 13th Army Group managed to expel the US Eighth Army from northwest Korea. Retreating from the north faster than they had counter-invaded, the Eighth Army crossed the 38th parallel border in mid December.^[134] The UN morale hit rock bottom when commanding General Walton Walker of the US Eighth Army was killed on 23 December 1950 in an automobile accident.^[135] In the northeast Korea by 11 December, the US X Corps managed to cripple^[136] the PVA 9th Army Group while establishing a defensive perimeter at the port city of Hungnam. The X Corps were forced to evacuate by 24 December in order to reinforce the badly depleted US Eighth Army to the south.^[137][138]

Map of the UN retreat in the wake of Chinese intervention

During the Hungnam evacuation, about 193 shiploads of UN Command forces and materiel (approximately 105,000 soldiers, 98,000 civilians, 17,500 vehicles, and 350,000 tons of supplies) were evacuated to Pusan.^[139] The SS Meredith Victory was noted for evacuating 14,000 refugees, the largest rescue operation by a single ship, even though it was designed to hold 12 passengers. Before escaping, the UN Command forces razed most of Hungnam city, especially the port facilities;^[105][140] and on 16 December 1950, President Truman declared a national emergency with Presidential Proclamation No. 2914, 3 C.F.R. 99 (1953),^[141] which remained in force until 14 September 1978.^[b]

Fighting around the 38th parallel (January – June 1951)[link]

With Lieutenant-General Matthew Ridgway assuming the command of the U.S. Eighth Army on 26 December, the PVA and the KPA launched their Third Phase Offensive (also known as the "Chinese New Year's Offensive") on New Year's Eve of 1950. Utilizing night attacks in which U.N. Command fighting positions were encircled and then assaulted by numerically superior troops who had the element of surprise. The attacks were accompanied by loud trumpets and gongs, which fulfilled the double purpose of facilitating tactical communication and mentally disorienting the enemy. UN forces initially had no familiarity with this tactic, and as a result some soldiers "bugged out," abandoning their weapons and retreating to the south.^[142] The Chinese New Year's Offensive overwhelmed UN forces, allowing the PVA and KPA to conquer Seoul for the second time on 4 January 1951.

B-26 Invaders bomb logistics depots in Wonsan, North Korea, 1951

These setbacks prompted General MacArthur to consider using nuclear weapons against the Chinese or North Korean interiors, intending radioactive fallout zones would interrupt the Chinese supply chains.^[143] However, upon the arrival of the charismatic General Ridgway, the esprit de corps of the bloodied Eighth Army immediately began to revive.^[144]

U.N. forces retreated to Suwon in the west, Wonju in the center, and the territory north of Samcheok in the east, where the battlefront stabilized and held.^[142] The PVA had outrun its logistics capability and thus was forced to recoil from pressing the attack beyond Seoul;^[145] food, ammunition, and materiel were carried nightly, on foot and bicycle, from the border at the Yalu River to the three battle lines. In late January, upon finding that the PVA had abandoned their battle lines, General Ridgway ordered a reconnaissance-in-force, which became Operation Roundup (5 February 1951)^[146]. A full-scale X Corps advance gradually proceeded while fully exploiting the UN Command's air superiority,^[147] concluded with the UN reaching the Han River and recapturing Wonju.^[146]

In mid-February, the PVA counterattacked with the Fourth Phase Offensive and achieved initial victory at Hoengseong. But the offensive was soon blunted by the IX Corps positions at Chipyong-ni in the center.^[146] Units of the U.S. 2nd Infantry Division and the French Battalion fought a short but desperate battle that broke the attack's momentum.^[146] The battle is sometimes known as the Gettysburg of the Korean War. The battle saw 5,600 Korean, American and French defeat a numerically superior Chinese force. Surrounded on all sides, the US 2nd Infantry Division Warrior Division's 23rd Regimental Combat Team with an attached French Battalion was hemmed in by more than 25,000 Chinese Communist Forces. United Nations Forces had previously retreated in the face of large Communist forces instead of getting cut off, but this time they stood and fought at odds of roughly 15 to 1.^[148]

U.S. Marines move out over rugged mountain terrain while closing with the hostile North Korean forces.

In the last two weeks of February 1951, Operation Roundup was followed by Operation Killer, carried out by the revitalized Eighth Army. It was a full-scale, battlefront-length attack staged for maximum exploitation of firepower to kill as many KPA and PVA troops as possible.^[146] Operation Killer concluded with I Corps re-occupying the territory south of the Han River, and IX Corps capturing Hoengseong.^[149] On 7 March 1951, the Eighth Army attacked with Operation Ripper, expelling the PVA and the KPA from Seoul on 14 March 1951. This was the city's fourth conquest in a years' time, leaving it a ruin; the 1.5 million pre-war population was down to 200,000, and people were suffering from severe food shortages.^[149][106]

On 1 March 1951 Mao sent a cable to Stalin, in which he emphasized the difficulties faced by Chinese forces and the urgent need for air cover, especially over supply lines. Apparently impressed by the Chinese war effort, Stalin finally agreed to supply two air force divisions, three anti-aircraft divisions, and six thousand trucks. PVA troops in Korea continued to suffer severe logistical problems throughout the war. In late April Peng Dehuai sent his deputy, Hong Xuezhi, to brief Zhou Enlai in Beijing. What Chinese soldiers feared, Hong said, was not the enemy, but that they had nothing to eat, no bullets to shoot, and no trucks to transport them to the rear when they were wounded. Zhou attempted to respond to the PVA's logistical concerns by increasing Chinese production and improving methods of supply, but these efforts were never completely sufficient. At the same time, large-scale air defense training programs were carried out, and the Chinese Air Force began to participate in the war from September 1951 onward.^[150]

Chinese soldiers captured by Australians, 24 April 1951.

On 11 April 1951, Commander-in-Chief Truman relieved the controversial General MacArthur, the Supreme Commander in Korea.^[151] There were several reasons for the dismissal. MacArthur had crossed the 38th parallel in the mistaken belief that the Chinese would not enter the war, leading to major allied losses. He believed that whether or not to use nuclear weapons should be his own decision, not the President's.^[152] MacArthur threatened to destroy China unless it surrendered. While MacArthur felt total victory was the only honorable outcome, Truman was more pessimistic about his chances once involved in a land war in Asia, and felt a truce and orderly withdrawal from Korea could be a valid solution.^[153] MacArthur was the subject of congressional hearings in May and June 1951, which determined that he had defied the orders of the President and thus had violated the US Constitution.^[154] A popular criticism of MacArthur was that he never spent a night in Korea, and directed the war from the safety of Tokyo.^[155]

General Ridgway was appointed Supreme Commander, Korea; he regrouped the UN forces for successful counterattacks,^[156] while General James Van Fleet assumed command of the US Eighth Army.^[157] Further attacks slowly depleted the PVA and KPA forces; Operations Courageous (23–28 March 1951) and Tomahawk (23 March 1951) were a joint ground and airborne infilltration meant to trap Chinese forces between Kaesong and Seoul. UN forces advanced to "Line Kansas," north of the 38th parallel.^[158] The 187th Airborne Regimental Combat Team ("Rakkasans") second of two combat jumps were on Easter Sunday, 1951 at Munsan-ni, South Korea codenamed Operation Tomahawk. The mission was to get behind Chinese forces and block their movement north. The 60th Indian Parachute Field Ambulance provided the medical cover for the operations, dropping an ADS and a surgical team and treating over 400 battle casualties apart from the civilian casualties that formed the core of their objective as the unit was on a humanitarian mission.