The J60 conception and project design began in July 1957 at United Aircraft of Canada (now Pratt & Whitney Canada) in Montreal. The project design details were transferred to the main P&W company in East Hartford and in May 1958, the first prototype, with military designation YJ60-P-1 commenced testing.
Flight tests were completed in early 1959; followed by the delivery of the new JT12A-5 engines in July 1959. These were for the two Canadair CL-41 prototype trainers with a rating of 12.9 kN (2,900 lb st). The modified JT12A-3 turbojets with a basic rating of 14.69 kN (3,300 lb st) were tested in the two Lockheed XV-4A HummingbirdVTOL research aircraft. The next version, JT12A-21, had an afterburner which delivered a maximum thrust of 17.91 kN (4,025 lb st).