Anti-submarine warfare
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Anti-submarine warfare is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations are typically carried out to protect friendly shipping and coastal facilities from submarine attacks and to overcome blockades.
Royal Navy officers on the bridge of a destroyer on convoy escort duties keep a sharp look out for enemy submarines during the Battle of the Atlantic, October 1941
An example of an anti-submarine net, once protecting Halifax Harbour, Canada.
11-inch Howitzer Mk. I on British armed merchant cruiser HMS Patia in 1918, it had a range of just about 600 yards (550 m)
A depth charge thrower being loaded, aboard corvette HMS Dianthus, 14 August 1942
Sonobuoy
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A sonobuoy is a small expendable sonar buoy dropped from aircraft or ships for anti-submarine warfare or underwater acoustic research. Sonobuoys are typically around 13 cm (5 in) in diameter and 91 cm (3 ft) long. When floating on the water, sonobuoys have both a radio transmitter above the surface and hydrophone sensors underwater.
Hand deployment of a sonobuoy in the Arctic Ocean from the aft deck of the R/V Sikuliaq
P-3 Orion paradropping a sonobuoy
AN/SSQ-47B active pinger ranging sonar sonobuoy (frequency #4) and shipping container (octagonal form aids stacking)