 Westland Helicopters, which had a long-standing licence agreement with Sikorsky Aircraft to allow it to build Sikorsky's helicopters, extended the agreement to cover the Sikorsky SH-3 Sea King soon after the Sea King's first flight in 1959. Westland proceeded to independently develop the Sea King, integrating a significant proportion of components from British suppliers; key changes include the use of a pair of Rolls-Royce Gnome turboshaft engines and the implementation of an automatic flight control system. On this matter, authors Jim Thorn and Gerald Frawley stated that: "Despite appearances, Westland's Sea King [is a] very different aircraft from Sikorsky's". Many of the differences between the Westland-built Sea King and the original helicopter were as a result of differing operational doctrine. While the U.S. Navy Sea Kings were intended to be under tactical control of the carrier from which they operated, the Royal Navy intended its helicopters to be much more autonomous, capable of operating alone, or coordinating with other aircraft or surface vessels. This resulted in a different crew arrangement, with operations being controlled by an observer rather than the pilot, as well as fitting a search radar.
