In 1966, the USAF awarded a contract to Sikorsky for development of a minimum-change CSAR variant of the CH-53A. It featured a retractable inlfight refueling probe, jettisonable external fuel tanks mounted to the outside of the sponsons, a rescue hoist above the crew entry door, armor plating, a Doppler navigation radar and three pintle mounted GAU-2/A 7.62mm miniguns for self defence. First flight: 15 March 1967. Early HH-53Bs featured T64-GE-3 turboshafts with 3,080 shaft horsepower (2,297 kW), but these engines were later upgraded to T64-GE-7 turboshafts with 3,925 shaft horsepower (2,927 kW).
The HH-53B first flew from Stratford, CT on 15 March 1967.