The Westland Sea King was one among a family of very successful military helicopters which began life as the Sikorsky SH-3 anti-submarine platform for the US Navy and later license produced in the UK. The Sea King was unique in having a boat-like hull which actually permitted it to remain afloat in case of an emergency as well as remarkable performance figures: it was the first helicopter to exceed 200 mph in flight and also held the longest non-stop distance record (from offshore carriers in San Diego to Jacksonville). It's primary mission was anti-submarine warfare and thus was equipped with dipping sonar systems, sonobuoys, and a magnetic anomaly detector (MAD) in addition to carrying torpedoes or anti-ship missiles. Aside from these roles, however, British-built Sea Kings have also been used as tactical troop transports with significant air-to-surface attack capability. Overall they have been used for a wider number of mission requirements than their US counterparts and have seen extensive action in the Falklands, the Gulf War, the Balkans, and more recently in the Iraq War.

Developed from the Sikorsky S-61, the Sea King prototype HSS-1 made its first flight on 11 March 1959 and eventually captured the interest of British authorities which signed a license agreement resulting in the first Westland-assembled unit flying in 1967. The Sea King HAS.1 had minimal fuselage changes to its US counterpart but had Rolls-Royce engines and other local avionics while an engine upgrade led to the HAS.2, also developed as an early-warning platform known as the AEW.2A with a large side-mounted radome below the hull. Other naval versions included the HAR.3 for search and rescue (SAR), the HAS.5 with advanced ASW capability and a prominent search radar, and the ultimate HAS.6 with composite main rotor blades, strenghtened airframe and transmission, advanced avionics, and the ability to carry the Sea Eagle anti-ship missile. Meanwhile, a land-based development (originally designed for export to the Middle East as the Commando Mk. 1 and Mk. 2) led to HC.4, essentially a tactical transport version for the Royal Navy with substantial attack capabilities including guns, rockets, and missiles.