Submarine

At the beginning of the 20th century, the submarine equipment was gradually improved and its performance was gradually improved. Submarines with certain combat capabilities appeared. These submarines adopt double hull, with good airworthiness, displacement of hundreds of tons, and use diesel-electric dual propulsion system. The speed on the surface is about 10-15 knots, and the underwater speed is 6-8 knots, and the endurance is significantly improved; The weapons mainly include artillery, torpedo and torpedo. Before the First World War, the major naval countries had more than 260 submarines, which became one of the important combat forces of the Navy.

At the beginning of the First World War, submarines were used in combat. On September 22, 1914, the German U-9 submarine sank three British cruisers in succession within more than one hour, fully demonstrating the submarine's combat power. During the war, submarines from all countries sank a total of 192 combat ships. The use of submarines to attack the transport merchant ships on the ocean traffic line has achieved more remarkable results. Submarines from various countries have sunk more than 5000 merchant ships, up to 14 million tons. About 13 million tons of merchant ships were sunk by German submarines. At the same time, anti-submarine warfare began to receive attention. During the war, 265 submarines were sunk, of which Germany lost more than 200.

The first submarine used for military purposes appeared in the American War of Independence. David Bushnell of Yale University in the United States built the Turtle, and filled the water tank with water through the pedal valve, which can make the boat submerge to 6 meters underwater and stay underwater for about 30 minutes. The boat is equipped with two hand-crank propellers, which enable the boat to obtain a speed of about 3 knots and control the lifting and lowering of the boat. There is a hand-operated pressure pump in the boat to discharge the water in the water tank and float the boat. An explosive bag that can be detonated by a time fuse is carried outside the boat, and can be controlled and tied to the bottom of the enemy ship inside the boat. Only one person can operate the rudder and propeller inside. In 1776, the Turtle attempted to attack the HMS Eagle. Although it was unsuccessful, it initiated the first attempt of a submarine to attack a warship.