OVERVIEW: The WE.177A (Type A) is an aerial-deployed nuclear depth charge developed by the United Kingdom in 1966. It served as a tactical nuclear weapon for anti-submarine warfare.

DETAILS: WE.177A is the smallest variant of the WE.177 series, weighing approximately 272 kg with a streamlined casing and stabilizing fins. It can be parachute-retarded or free-fall deployed from fixed-wing aircraft and helicopters. The weapon features selectable yield settings for shallow/submarine depth and deeper-water or surface burst achieved via hydrostatic depth sensing near 40 ft. The WE.177A remained in service from 1966 until its withdrawal in 1992.

FUNCTION: The WE.177A is dropped by ASW aircraft or helicopters upon sonar or MAD detection, sinking to preset depth before detonation. Its purpose is to destroy or incapacitate enemy submarines through nuclear shock waves.

NOTE:
IOC: September 1966
Operators: United Kingdom (Royal Navy, RAF)
Platforms: Fixed-wing (Sea Harrier, Buccaneer, TSR‑2 prototype, Tornado) and rotary-wing (Sea King, Westland Wasp) aircraft 
Conflict used in: None confirmed; deployed during the Falklands War (1982) but not used 

SOURCE:
Wikipedia: WE.177 ; NuclearWeaponArchive – Britain’s Nuclear Weapons; National Museum of Nuclear Science & History; Nuclear Weapon Archive; Naval archives.