Boeing P-26

The Boeing Company funded the project to produce the Boeing Model 248 in September 1931, with the US Army Air Corps supplying the engines and instruments. The design included an open cockpit, fixed landing gear and externally braced wings and it was the last of such design procured by the USAAC as a fighter aircraft. The original Model 248 had a very high landing speed which caused many accidents, so in order to remedy that, flaps were fitted to reduce landing speed. The USAAC ordered three prototypes, under the name of Boeing XP-936 with the first flight taking place on 20th March 1932.
The prototype was still hard to land and sometimes, due to its short nose, it rolled onto its back and would flip forward, injuring, or even killing, the pilot. The prototype's unarmed headrest offered virtually no protection in such cases, so the production model, called Model 266 (Boeing P-26A) had a taller armoured headrest installed.
The P-26A version was powered by a single Pratt & Whitney R-1340-27 "Wasp" with a power of 600hp while subsequent versions, the P-26B and C were powered by the R-1340-33 fuel-injected engines. The C version had modified and optimized fuel systems and all of them were armed with two 0.30in (7.92mm) M1919 Browning machine guns or one 0.30in and one 0.50in (12.7mm) calibre machine guns and could carry up to 90Kg (100lb) of bombs.
Back in the early 1930s it was the fastest American fighter aircraft to serve with the USAAC. However, as the aircraft technology was developing very quick, it soon became obsolete with wire-braced wings, fixed landing gear and open cockpit. For comparison purposes, the Dewoitine D.500 flew for the first time the same year as the P-26 and the Soviet Polikarpov I-16 was already flying with retractable landing gear by 1934, just two after the P-26. By 1935, just two year after the P-26 was designed, the Curtiss P-36, the Messerschmitt Bf.109 and the Hawker Hurricane, were all flying with enclosed cockpits, retractable landing gear and cantilever wings. However, as the P-26 was easy to flight, it remained in service with the USAAC until the United States entered the World War II.
It was delivered to the USAAC's Pursuit Squadrons in December 1933 with the last production aircrafts rolling out of the factory in 1936, under the designation of P-26C. Twenty-two squadrons flew the P-26, with peak service being six squadrons in 1936. They were the frontline fighter of the USAAC until 1938 when the Curtiss P-36 and the Seversky P-35 began to replace the P-26. Twenty of them were lost in accidents between 1934 and 1941, but only five before 1940.
They were also assigned to overseas deployment to supplement the Seversky P-35 at Wheeler Field, in Hawaii between 1938 and 1940 and, while some of them remained there as trainers, others were sent to Albrook Field, in the Panama Canal Zone, were nine of them were active in December 1941. They also served with the 3rd Pursuit Squadron of the 4th Composite Group, based in the Philippines and they were sold between 1937 and 1941 to the Philippne Army Air Corps.

Sources:
1. https://en.wikipedia.org/wiki/Boeing_P-26_Peashooter
2. Salamander Books - The Complete Book of Fighters.