Pratt & Whitney Aircraft's last piston engine was the 28-cylinder R-4360. It was the largest piston engine that the company ever produced. The cylinders were in four rows, arranged in a spiral for better cooling. Later models developed 3207 kW (4,300 shp).

Although primarily known by its commercial designation as the Wasp Major, it mainly powered large American military aircraft, including late entry Boeing B-29s, Boeing B-50 and C-97, Douglas C-124, Fairchild C-119, and Convair B-36. It had only one well known civil application in the Boeing Stratocruiser, which was derived from the C-97 and B-50. The Wasp Major was a complex engine, with maintenance problems particularly significant in the B-36 that used six of these engines.

The R-4360-4 passed its military qualification test in January 1945. This Navy engine powered the: Goodyear F2G-1; Martin XBTM-1, AM-1, AM-2, XP4M-1, and JRM-2. The R-4360-4A powered the Hughes XF-11 and HFB-1 (H4) aircraft.