In March 1951 Pratt & Whitney began flight tests of its new 10,000-pound thrust J57 jet engine.
On May 25, 1953, a J57-powered YF-100A exceeded Mach 1 on its maiden flight. The engine was produced from 1951 to 1965 with a total of 21,170 built.
The J79 was developed in the 1950s as an outgrowth of the General Electric J73 engine program, originally called J73-GE-X24A, intended for reliable Mach 2 performance.
The first flight of the engine was on 20 May 1955 where the engine was placed in the bomb bay of a J47-powered B-45C (48-009). The J79 was lowered from the bomb bay and the four J47s were shut down leaving the B-45 flying on the single J79.
The first flight after the 50-hr qualification test was on 8 December 1955, powering the second pre-production Douglas F4D Skyray, with the J79 in place of its original Westinghouse J40 engine as part of the General Electric development and qualification program. The YF-104 was the next airplane to fly with the J79 followed by a re-engined Grumman F11F Tiger in a Navy-sponsored program to gain experience with the engine before the first flight of the F4H (F-4).
The first flight of the YB-58 (55-0660) with 4 YJ79-GE-1 engines was made on 11 November 1956.