Landing Ship Medium were amphibious assault ships of the United States Navy in the World War II.
Of comparable size to Landing Ship, Tank and the Landing Craft, Infantry, there were 558 LSM (Landing Ship, Medium) made for the USN between 1944 and 1945. The majority of vessels built on this versatile frame were regular transports however there were several dozen that were converted during construction for specialized roles. Most vessels of this type were scrapped during the Cold War, but several were sold by the United States Department of Defense to foreign nations or private shipping companies.
Only one LSM, USS LSM-45 is known to still exist in its original configuration. It is in storage at Marine Station Camp Lejeune in Jacksonville, NC. It was slated to become the centerpiece of the Museum of the Marine, but due to changed plans, is now in danger of being scrapped or sunk as an artificial reef.
An amphibious warfare ship (or amphib) is a warship employed to land and support ground forces, such as marines, on enemy territory during an amphibious assault. The largest fleet of these types is operated by the United States Navy, including the Tarawa class amphibious assault ships dating back to the 1970s and the newer and larger Wasp class ships that debuted in 1989.
The history of the specialist amphibious assault vessel really begins during World War II. Prior to World War I, amphibious assaults had taken place using conventional boats. The disastrous Gallipoli landings of 1915 showed that this type of operation was impossible in the face of modern weapons, especially the machine gun. The 1920s and 1930s did not see much progress in most of the world, the exception being by the United States Marine Corps. Small-scale operations conducted by the Marine Corps in Latin America in the 1920s and 1930s, known as the Banana Wars, led to the development of advanced amphibious assault doctrine. By the late 1930s, concrete plans were beginning to form to build the first true specialized amphibious assault ships.