In June 1925, before the first of the Boeing PW-9s ordered in 1924 had been delivered, the USAAS decided to have the 30th and last PW-9 [25-324] modified during production to test high-altitude performance of the new turbo-supercharged 510hp Packard 1A-1500. This modification was considered important enough to warrant a designation change to XP-4 in accordance with the new system that had just been adopted.

    The XP-4 had a new, more aerodynamic wing profile, with both wings being of equal size and larger than those of the PW-9 in order to provide the necessary larger area needed to lift the increased weight. A fuselage-mounted pair of .30 machine guns was supplemented by two extra .30 s mounted in the lower wing, situated far enough outboard to clear the propeller arc. A four-bladed propeller was fitted. The new engine made it necessary to redesign the cowling, and the turbosupercharger was mounted externally on the right-hand side.

The XP-4 was delivered to the Army at Wright Field for tests on July 27, 1926. The Packard engine did not prove to be sufficiently powerful to compensate for the 800# increase in empty weight, and the performance of the XP-4 was rather disappointing. It did, in fact, actually perform more poorly than did the standard PW-9, and the XP-4 project was abandoned after only four hours of flying time. The airframe was surveyed on May 1, 1928.

    Empty weight was 2711# with gross weight 3603#. Maximum speed was 161mph. Initial climb rate was 2055 fpm. Service ceiling was 22,000', range was 375 miles.