Sikorsky CH-3E helicopter model. The CH-3E was the USAF version of the Sikorsky S-61 amphibious transport helicopter developed for the U.S. Navy. The USAF initially operated six Navy HSS-2 (SH-3A) versions of the S-61 in 1962, eventually designating them CH-3A/Bs. They were so successful the USAF ordered 75, modified as CH-3Cs, featuring a new rear fuselage design with a ramp for vehicles and other cargo. The first CH-3C was flown on June 17, 1963. When 41 CH-3Cs were updated with more powerful engines in 1966, they were redesignated as CH-3Es. Forty-five more were newly manufactured. Later, 50 CH-3Es were modified for combat rescue missions with armor, defensive armament, self-sealing fuel tanks, a rescue hoist, and in-flight refueling capability. They were redesignated HH-3Es and used extensively in Vietnam under the nickname "Jolly Green Giant."