Many attempts by many American companies were made to replace outmoded and outgoing fighters in service to the United States Army Air Corps (USAAC) in the lead-up to World War 2 (1939-1945). However, many such attempts from even the most prominent of military aviation companies fell by the wayside. Curtiss, largely remembered for its early-war entry over China - the P-40 "Warhawk" - put forth a bevy of possible fighter designs to the Army both pre-war and during the conflict. However, none met the level of success that the P-40 found, the XP-60 being one such entry into Curtiss' long and storied history.
The new fighter design, known in-house as "Model 90", was showcased to Army officials in January of 1941 - eleven months before the American entry into World War 2. The aircraft was built around the existing frame of the P-40 (P-40D) though with a more streamlined nose section (thanks to a relocated radiator) and an all-new laminar flow wing. Power was to come from the Rolls-Royce Merlin 28 inline engine - built stateside as the Packard V-1650-1 - a single-stage, supercharged engine of 1,300 horsepower output driving a three-bladed propeller unit from Curtiss-Electric. Seating was for one and a "tail-dragger" undercarriage retained - the latter carried over from another Curtiss fighter project - the XP-46 of which only two were constructed. Proposed armament became 8 x 0.50 caliber heavy machine guns.
In less than a year, a ground trials of the new aircraft - designated "XP-60" - were already underway with a first flight recorded on September 18th, 1941. Test flying revealed some required changes though these only proved slight to the overall design form of the aircraft. In March of 1943, the aircraft was handed over to Army authorities for formal testing but it was during this period that several setbacks were encountered centering on the undercarriage. Performance from the design, coupled with its Packard engine, was also not impressive.
While the XP-60 was still in development, thought was already being given to a better-performing version which resulted in the "XP-60A". This aircraft carried a turbosupercharged Allison V-1710-75 of 1,425 horsepower output which forced the XP-60's design form to be rewritten some. With Army interest piqued in this new offering, the service commissioned for 1,950 of the fighter as the production "P-60A" in October of 1941. However, the P-60A also revealed its own performance limitations despite the alternate engine being fitted. With the Japanese attack on Pearl Harbor thrusting the United States into war, the commitment to the P-40 product ruled P-60A production out and the initiative was cancelled at the beginning of 1942.
Even with this unexpected move, the XP-60A was allowed to continue in development though purely along experimental lines. This included the aircraft being outfitted with a four-bladed propeller unit and alternate wings. The aircraft was now known to Curtiss as "Model 95A".
Following XP-60A came XP-60B as "Model 95B". This example mounted a Wright turbosupercharger but was more or less the same product. The XP-60C ("Model 95C") was brought along with an experimental Chrysler XIV-2220 liquid-cooled engine in a slightly more portly airframe. The addition of the Chrysler engine showcased some drawbacks to the design which was now becoming overweight. This prompted a move to the Pratt & Whitney R-2800 "Double Wasp" air-cooled radial.
Work progressed on the original XP-60 to the point that a supercharged Merlin 61 series inline was now fitted and the variant was redesignated as "XP-60D". However, this airframe was lost in an in-flight accident on May 6th, 1943 during a diving demonstration. The XP-60A suffered its own mishap in October of 1942 when an engine fire grounded it and forced some speedy modifications. A first flight followed in November. That same month, the airframe was removed from active testing and cannibalized for parts.
The XP-60C was able to secure a new Army contract later that month for 500 production-quality aircraft in a "P-60A-1" guise. The switch to a Pratt & Whitney powerplant offered promising performance gains and the lot would include both single-prop and contra-rotating prop forms for both evaluation and standard service use. Armament for both versions centered on 4 x 0.50 caliber heavy machine guns. A new variant emerged as the XP-60E which fitted a PW R-2800-10 with a four-bladed propeller and GE turbosupercharger though this model saw very little life. The XP-60C - with the odds stacked against it - competed unsuccessfully against other types in a USAAF (United States Army Air Forces) fly off. The government ended its interest in the P-60 as a production aircraft on June 3rd, 1943.
Development of the XP-60E continued at least until January 1944. The aircraft was then tested by the Army and fared poorly when compared to existing offerings seeing actual combat service in the war. one final form then emerged, interestingly at the behest of the Army, and this aircraft was given the developmental designation of "YP-60E". The lines of the P-40 were all but gone from this model as it carried an appearance more akin to the Republic P-47 "Thunderbolt" by this point - low rounded wing mainplanes, a deep fuselage, four-bladed propeller, and a bubble canopy YP-60E flew once for the USAAF and was written off in December of 1944. Another proposed XP-60 form became the XP-60F which was to carry an alternate version of the PW R-2800 series engine. This was not furthered.
By this time, the service was doing quite well with its stable of modern fighters that had evolved to also become effective fighter-bombers - the P-47, North American P-51 "Mustang", and the Lockheed P-38 "Lightning" were all used to excellent effect over Europe and elsewhere. 1944 also served as a turning-of-the tide for the Allies which resulted in the end of the war in Europe during May of 1945. The Pacific War followed in August of that year.
The XP-60 program was a long and arduous one with very little result to show for itself by the end of it all. It joined a long line of abandoned (or cancelled) Curtiss products that never would match the popularity of its "Warhawk".