The P-60 program was a final attempt to produce a replacement for the P-40 Warhawk. It began in 1941, when one of the XP-53 prototypes was re-engined to use a Packard Merlin engine. However, during 1941 it became clear that there would not be enough Merlin engines to spare, and so the XP-60 was re-engined again to use the Allison V-1710-75 engine. This version was even ordered into production – 1950 were ordered on 31 October 1941, but the order was soon cancelled in favour of the P-47 Thunderbolt.
A variety of other engine combinations were investigated before the P-60 program was cancelled in 1944. The XP-60C was first developed to use a Chrysler engine, but was completed using the Pratt & Whitney R-2800 radial engine. A second Pratt & Whitney powered aircraft, the XP-60E even led to the production of a service test aircraft in 1944, designated YP-60E, but despite all the effort put into it, this new aircraft was not as good as existing designs, including the P-51 Mustang that had used up so many Packard Merlin engines in 1941. The P-60 program was finally cancelled in mid 1944.