.jpg "Anti Submarine Aircraft/(s3)")
Anti-submarine warfare (ASW, or in older form A/S) is a branch of underwater warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines.
Successful anti-submarine warfare depends on a mix of sensor and weapon technology, training, and experience. Sophisticated sonar equipment for first detecting, then classifying, locating and tracking the target submarine is a key element of ASW. To destroy submarines both the torpedo and mine are used, launched from air, surface and underwater platforms. Other means of destruction have been used in the past but are now obsolete. ASW also involves protecting friendly ships.
The first attacks on a ship by an underwater vehicle are generally believed to have been during the American Revolutionary War, using what would now be called a naval mine but what then was called a torpedo, though various attempts to build submarines had been made before this. The first self-propelled torpedo was invented in 1863 and launched from surface craft. The first submarine with a torpedo was Nordenfelt I built in 1884-1885, though it had been proposed earlier. In the Russo-Japanese War of 1904-5, the submarine was a significant threat. By the start of the First World War nearly 300 submarines were in service. Some warships were fitted with an armoured belt as protection against torpedoes.