The Curtiss XP-23 was the last biplane fighter design to be produced by the Curtiss company, and was perhaps one of the best-looking fighter biplanes ever produced by any manufacturer.
The last P-6E in the USAAC order (Ser No 32-278) had been held back at the Curtiss factory for tests. It was completed with an entirely new monocoque aluminum fuselage, new tail surfaces, a new nose, new landing gear, and a turbosupercharged and geared Curtiss G1V-1570-C engine. A three-bladed propeller was fitted. The nose was much sharper and more pointed than that of the P-6E, giving a much more aerodynamically-clean appearance. The cooling radiator was mounted on the underside of the fuselage between the landing gear legs, just as it was on the P-6E. The wings had the same design as the P-6E, but were of all-metal construction rather than wood. However, the wings still had a fabric covering.
The result was an airplane quite different in appearance from the P-6E. Since it was essentially a new design, the aircraft was redesignated XP-23 by the USAAC. The XP-23 was delivered to the USAAC on April 16, 1932. Weights were 3274 lb empty, 4124 lb gross. Maximum speed was 180 mph at sea level, 223 mph at 15,000 feet. Initial climb was 1370 ft/min, service ceiling was 33,000 feet, and range was 435 miles. Armament was one 0.50-cal and two 0.30-cal machine guns, all mounted in the nose.
Although the XP-23 was the fastest biplane fighter yet produced and had an improved altitude performance, the USAAC recognized that the era of the biplane fighter had finally come to an end. Since they had already ordered the Boeing P-26A monoplane fighter, the Army opted not to go ahead with an order for production examples of the P-23.
Even though no production orders were forthcoming, tests still continued with the XP-23. The XP-23 designation was switched to YP-23 when the status changed from "experimental" to "service test". As YP-23, it had its supercharger removed and the three-bladed propeller was replaced by a two-bladed unit. This airplane was later used in a rather interesting test to determine the effects of radiator drag on high-speed aircraft. For a brief period, the aircraft was flown without any radiator at all, the cooling water being pumped through the engine from an isolated tank and discharged overboard rather than being recirculated.