Following the failure of the XP-46 to win any Army production orders, the Curtiss company proposed another design in their search for the eventual replacement for the P-40.
This was the Curtiss Model 88, which was an improved XP-46 powered by the yet-to-be-built 1600-hp Continental XIV-1430-3 twelve-cylinder liquid-cooled inverted V-engine.
The Model 88 was to use the fuselage and tail assembly from the P-40D combined with a NACA laminar flow wing.
Armament was to have consisted of eight wing-mounted machine guns.
The mainwheel retraction scheme reverted to the sequence used by the original P-40, with the mainwheels rotating 90 degrees before they retracted rearwards into wing wells.
Maximum speed was projected to be 430 mph.
On October 1, 1940, the USAAC ordered two examples of the Model 88 under the designation XP-53.
Serials were 41-140 and 41-19508.
In a conference held six weeks later, the USAAC informed Curtiss-Wright of its need for a fighter combining laminar flow wing technology with the British Rolls-Royce Merlin engine.
Since the XP-53 was already being designed for laminar-flow wings, Curtiss proposed to convert the second XP-53 airframe (41-19508) to the Merlin engine while it was undergoing construction.
This airframe was redesignated Model 90 by the company.
The USAAC accepted this idea, and assigned the designation XP-60 to the new aircraft. The other XP-53 airframe was to retain the Continental engine.
However, while the XP-53 and XP-60 were both undergoing construction, the Army cancelled the XP-53 order because of the excessive delays in the temperamental Continental XIV-1430 engine.
The XP-53 never flew. As it turned out, the Continental engine never did enter production, and all of those aircraft projects which had planned for it ultimately failed.
In November 1941, the XP-53 airframe was converted into a static test airframe in support of the P-60 project, and its bullet-proof windshield, self-sealing fuel tanks, and armament were scavenged and transferred to the XP-60.
During construction of the XP-60 aircraft, it was decided to replace the rearward- retracting P-40 style landing gear with a new inward-retracting gear similar to that which had been fitted to the abortive XP-46.
Initially, the XP-60 was fitted with a British-built Merlin 28 engine.
The Model 90 (XP-60) flew for the first time on September 18, 1941, only eleven days before the first flight of the disappointing XP-46.
The performance of the XP-60 was disappointing as well, with a top speed of only 387 mph at 22,000 feet.
It took 7.3 minutes to reach an altitude of 15,000 feet, and service ceiling of 29,000 feet. Some of the reason for the disappointing performance was due to the wing surface not being finished to the degree of smoothness required for the laminar flow wing.
Another factor was the fact that the Merlin engine did not deliver the guaranteed output.
Empty weight was 7008 pounds, gross weight was 9277 pounds, and maximum take-off weight was 9700 pounds.
Dimensions were wingspan 45 feet 5 1/4 inches, length 33 feet 7 1/2 inches, height 12 feet 4 inches, and wing area 275 square feet.