What did the Sea King bring that was new to US Navy anti-submarine warfare?

In 1957 Sikorsky received a contract to produce an all-weather amphibious helicopter for the US Navy. Instead of the HSS-1F, the company was able to offer the Navy the HSS-2, an entirely new design carefully tailored to the anti-submarine mission. The Navy, Sikorsky and the Pacific Division of Bendix Aviation Corp. developed helicopter anti-submarine warfare technology, combining the speed of an aircraft with the underwater sonar that until then had been carried aboard ships.

The aircraft combined the hunter and killer roles, which had previously been split between two helicopters. It was the first operational US helicopter able to search for and destroy submarines at the same time. Its equipment included the AQS-13 sonar, with a 180-degree search beam, the Ryan APN-130 Doppler radar and radar altimeter, and Hamilton Standard auto-stabilisation equipment.

Its new engine almost quadrupled the power-to-weight ratio of the previous engine in a compact package one sixth of its size, and that allowed Sikorsky to tailor a helicopter to a mission for the first time. In June 1966 an order for 60 SH-3D Sea Kings was placed with Westland. By 1979, the Royal Navy had ordered 56 HAS1s and 21 HAS2s to meet its anti-submarine needs.