Following rejection of the XP-46, Curtiss put forward its Model 88 in proposals to the
United States Army Air Corps. The proposal was for an aircraft using the P-40D fuselage and tail assembly with a low drag NACA
laminar flow wing, the (at the time under development)
Continental I-1430-3 inverted V-12 engine, and eight wing-mounted 0.5 in (12.7 mm) machine guns. This proposal was accepted and a contract for two
prototypes was issued on 1 October 1940 with the aircraft designated
XP-53. Within two months the Army Air Corps contacted Curtiss for an aircraft with a laminar wing and the British
Rolls Royce Merlin engine. Curtiss suggested the XP-53 design be used and the second prototype be converted while it was being built; the contract was altered to account for that with the aircraft - known to the company as Model 90 - designated
XP-60. A Packard-built V-1650-1 (equivalent to the Merlin Mk XX) as being used on the Curtis XP-40F was to be used. Flight tests of the XP-60 prototype did not progress smoothly. In addition to landing gear problems, expected top speed was not being met due to shortcomings in the laminar-flow wing surface finish, relatively high
radiator drag (compared to the
North American P-51 Mustang, which was then flying), and lower than specified engine output performance. The P-60A Allison engine was not delivering the requisite 1,500 hp, and now that America was at war following the Japanese attack on Pearl Harbor, delivery of existing designs took precedence over introducing a new design into production. Work on the P-60A was stopped after 20 December 1941, when the USAAF recommended that Curtiss concentrate on license production of
Republic P-47 Thunderbolts. The P-60 project was not stopped but a decision was taken to build experimental aircraft on the XP-60 but with different engines. - the Thunderbolt for the USAAF. At the time, availability of the Chrysler engine was coming into question, and after Curtiss noted (in April) that either the fuselage would need changes, or several hundreds of pounds of ballast would be needed in the tail of the existing airframe, to balance the heavy engine, a decision was made in September to install a
Pratt & Whitney R-2800 radial engine in the XP-60C. In the meantime, Curtiss installed a Packard V-1650-3 (equivalent of the Merlin 61) in the original XP-60 with a four bladed propeller and the larger XP-60A vertical stabilizer; this aircraft was redesignated
XP-60D. The XP-60A first flew on 1 November 1942. While official interest in the type was waning (with the emergence of newer designs), the promise of improved performance from use of the R-2800 engine, resulted in a contract for 500 aircraft, officially designated
P-60A-1, with the R-2800 and contra-rotating
propellers; the first 26 to be YP-60A with single rotation propeller. With concern that the contra-rotating propellers would not be available on time (Pratt & Whitney had to modify the engine gearing), in order to get data, the XP-60B was modified to take the R-2800-10 engine with turbocharger driving a four-bladed propeller. As a result of the other prototype variants, this modification was redesignated
XP-60E (Model 95D). On 27 January 1943, the XP-60C flew for the first time, powered by an R-2800-53 engine with contra-rotating propellers. The aircraft's flying characteristics were found to be generally satisfactory. The first flight of the XP-60E with the four-bladed propeller was delayed until 26 May 1943 after it was found that due to its lighter weight, the engine installation had to be moved forward compared to the XP-60C. In April 1943, the US Army Air Forces decided to conduct an evaluation of the various fighter aircraft in development and use, in order to eliminate the least desirable models. With four days notice Curtiss was requested to have the XP-60E participate. As the XP-60E was not available, the company hurriedly prepared the XP-60C (at the time being repaired) for the evaluation at
Patterson Field. The XP-60C performed poorly due to flaking wing finish preventing laminar flow and the engine delivering less power resulting in reduction of the production run of 500 aircraft to 20 YP-60A then to just two aircraft. On 6 May 1943, the XP-60D crashed during a dive demonstration. In January 1944, the XP-60E was flown to
Eglin Field for official trials, where USAAF pilots found that it did not compare favorably to contemporary aircraft designs. However, when Curtiss suggested abandoning future work on the P-60 series, the USAAF insisted on completion of at least one of the two aircraft already in production. ==Operational history==