Underwater

Underwater refers to the region below the surface of water where the water exists in a natural feature (called a body of water) such as an ocean, sea, lake, pond, or river.

Extent

Three quarters of the planet Earth is covered by water. A majority of the planet's solid surface is abyssal plain, at depths between 4,000 and 5,500 metres (13,100 and 18,000 ft) below the surface of the oceans. The solid surface location on the planet closest to the centre of the orb is the Challenger Deep, located in the Mariana Trench at a depth of 10,924 metres (35,840 ft). Although a number of human activities are conducted underwater—such as research, scuba diving for work or recreation, or even underwater warfare with submarines, this very extensive environment on planet Earth is hostile to humans in many ways and therefore little explored. But it can be explored by sonar, or more directly via manned or autonomous submersibles. The ocean floors have been surveyed via sonar to at least a coarse resolution; particularly-strategic areas have been mapped in detail, in the name of detecting enemy submarines, or aiding friendly ones, though the resulting maps may still be classified.

Navy

A navy or maritime force is a fleet of waterborne military vessels (watercraft) and its associated naval aviation, both sea-based and land-based. It is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake-borne, riverine, littoral, or ocean-borne combat operations and related functions. It includes anything conducted by surface ships, amphibious ships, submarines, and seaborne aviation, as well as ancillary support, communications, training, and other fields; recent developments have included space-related operations. The strategic offensive role of a navy is projection of force into areas beyond a country's shores (for example, to protect sea-lanes, ferry troops, or attack other navies, ports, or shore installations). The strategic defensive purpose of a navy is to frustrate seaborne projection-of-force by enemies. The strategic task of the navy also may incorporate nuclear deterrence by use of Submarine-launched ballistic missiles. Naval operations can be broadly divided between riverine and littoral applications (brown-water navy), open-ocean applications (blue-water navy), and something in between (green-water navy), although these distinctions are more about strategic scope than tactical or operational division.

Vessel

Vessel or vessels may refer to:

Biology

Container

Watercraft

Art, entertainment, and media

Music

Groups

Abums

Songs

Polish Navy

The Polish Navy (Polish: Marynarka Wojenna, "navy") is the military branch of the Polish Armed Forces responsible for naval operations. The current navy consists of 113 ships (including 5 submarines, 2 frigates, 1 corvette, 3 missile boats - as of 2014) and about 18,000 commissioned and enlisted personnel. The traditional ship prefix in the Polish Navy is ORP (Okręt Rzeczypospolitej Polskiej, "Vessel of the Republic of Poland").

The Polish Navy is one of the largest navies on the Baltic Sea and one of the best equipped. It is mostly responsible for Baltic Sea operations. Other duties include search and rescue operations covering parts of the Baltic, as well as hydrographic measurements and research.

Origins

The Polish Navy has its roots in naval vessels that were largely used on Poland's main rivers in defense of trade and commerce. During the Thirteen Years' War (1454–66), this small force of inland ships for the first time saw real open sea combat. At the battle of Vistula Lagoon, a Polish privateer fleet defeated the Teutonic Knights Navy and secured permanent access to the Baltic Sea. The Second Peace of Thorn (1466) acquired for Poland the strategic naval city of Danzig (Gdańsk), and with it the means of maintaining a large fleet on the Baltic. In 1561, following a victory over Russian Naval forces in the Baltic, the Polish Navy acquired a second key port at Riga, in modern-day Latvia.

Naval mine

A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel. Naval mines can be used offensively—to hamper enemy shipping movements or lock vessels into a harbour; or defensively—to protect friendly vessels and create "safe" zones.

Description

Mines can be laid in many ways: by purpose-built minelayers, refitted ships, submarines, or aircraft—and even by dropping them into a harbour by hand. They can be inexpensive: some variants can cost as little as US$1000, though more sophisticated mines can cost millions of dollars, be equipped with several kinds of sensors, and deliver a warhead by rocket or torpedo.

Their flexibility and cost-effectiveness make mines attractive to the less powerful belligerent in asymmetric warfare. The cost of producing and laying a mine is usually anywhere from 0.5% to 10% of the cost of removing it, and it can take up to 200 times as long to clear a minefield as to lay it. Parts of some World War II naval minefields still exist because they are too extensive and expensive to clear. It is possible for some of these 1940s-era mines to remain dangerous for many years to come.