U.S. Army Air Corps
Deliveries to USAAC pursuit squadrons began in December 1933 with the last production aircraft in the series coming off the assembly line in 1936, designated the P-26C. Ultimately, 22 squadrons flew the Peashooter, with peak service being six squadrons in 1936. P-26s were the frontline fighters of the USAAC until 1938, when Seversky P-35s and Curtiss P-36s began to replace the P-26. A total of 20 P-26s were lost in accidents between 1934 and America's entry into World War II, but only five before 1940.
The first Boeing P-26 to experience major combat operation was the Chinese Model 281. On 15 August 1937, eight P-26/281s from the Chinese Nationalist Air Force 3rd Pursuit Group, 17th Squadron, based at Chuyung airfield, engaged eight out of 20 Mitsubishi G3M Nell medium bombers from the Kisarazu Air Group sent to attack Nanking. The Chinese Boeing fighters helped shoot down two of the four Japanese bombers destroyed that day without suffering any losses. Subsequent engagements between the Chinese Peashooter pilots and pilots of the Imperial Japanese Navy flying the Mitsubishi A5M "Claudes" were the first aerial dogfights and kills between all-metal monoplane fighter aircraft. A single P-26 was in service with the Spanish Republican Air Force during the Spanish Civil War of 1936–1939, but no aerial kills were recorded with this fighter aircraft. It was shot down in 1936.
By December 1941, U.S. fighter strength in the Philippines included 28 P-26s, 12 of which were operational with the 6th Pursuit Squadron of the Philippine Army Air Corps. Filipino-flown P-26s claimed one G3M and two or three Mitsubishi A6M2 Zeros before the last of the P-26s were burned by their crews on 24 December 1941.
Only nine P-26s remained airworthy, serving in the Panama Canal Zone. In 1942–43, the Fuerza Aérea de Guatemala acquired seven P-26s ostensibly by the U.S. government smuggling them in as "Boeing PT-26A" trainers to get around restrictions of sales to Latin American countries. The last two P-26s in service were still flying with Guatemala's Air Force until 1956, when they were replaced with P-51 Mustangs. The P-26's last combat operation was with the Guatemalan Air Force during a coup in 1954.
The P-26 was the last Boeing Company fighter aircraft to enter service until Boeing acquired McDonnell-Douglas with production and continuing support contracts for the Boeing F/A-18E/F Super Hornet in 2002. Between those aircraft, Boeing did produce the experimental XF8B in 1944 as well as the prototype YF-22 in 1991.