When the U. S. Army Air Corps issued specification No. X-609 in March 1937, Robert J. Woods, chief engineer at the Bell Aircraft Corporation, was ready. Two months later, Woods proposed the Bell Model 4 to meet this specification for a highly-maneuverable fighter airplane with good visibility, heavy firepower, exceptional takeoff and landing qualities, and better ground-handling than existing types. The AAC was impressed enough to award Bell a contract for a single prototype, designated XP-39, on October 7, 1937, and the P-39 was born.

When the U. S. Army Air Corps issued specification No. X-609 in March 1937, Robert J. Woods, chief engineer at the Bell Aircraft Corporation, was ready. Two months later, Woods proposed the Bell Model 4 to meet this specification for a highly-maneuverable fighter airplane with good visibility, heavy firepower, exceptional takeoff and landing qualities, and better ground-handling than existing types. The Air Corps was impressed enough to award Bell a contract for a single prototype, designated XP-39, on October 7, 1937, and the P-39 was born.

Woods designed the P-39 around one primary component--the 37mm cannon. Considerable trial and error was required to avoid sacrificing the important airframe and engine requirements, such as speed and maneuverability, to the cannon's weight, size, and recoil characteristics. One arrangement had the cockpit located behind both the engine and the cannon but poor visibility ruled out this version. The final scheme mounted the engine amidships behind the pilot and cannon. A long drive shaft connected the engine and propeller gearbox. The cannon was located between the pilot and the propeller so that the gun could fire through the propeller hub. Woods envisioned the large space under the cannon as a place to store the retractable nosewheel and the Airacobra became the first Air Corps single-engine airplane with a tricycle landing gear.

Bell built the XP-39, U. S. Army Air Corps serial number 38-326, at its plant in Buffalo, New York. When the new fighter made its first flight on April 6, 1939, a turbo-supercharged Allison V-1710-17 engine powered the aircraft to a speed of nearly 627.9 kph (390 mph) at 6,080 m (20,000 ft). Two months after the first flight, the National Advisory Committee on Aeronautics (NACA) at Langley, Virginia, studied the XP-39 and recommended a list of modifications. It was primarily interested in streamlining to reduce drag but the modifications they ordered increased the loaded weight by 114 kg (250 lb) to 2,903 kg (6,450 lb). Even more damning, NACA advised the Air Corps to remove the turbo-supercharger, and it apparently agreed, believing that an engine with a geared supercharger was close at hand. However, Allison was years away from fielding such a powerplant and when it did, newer and more advanced airframes became the logical recipients. Without this vital component, the P-39 became unsuitable for combat above about 6,080 m (20,000 ft).

With war clouds gathering, the Air Corps contracted with Bell for eighty production airplanes designated the P-39C (twenty airplanes) and the P-39D (sixty airplanes). To supplement the cannon, Bell armed the P-39C with two .50 and two .30 caliber machine guns mounted in the upper nose cowling to fire through the propeller. The company relocated the .30 caliber gun battery to the wings and doubled their number on the P-39D. Foreign air forces, debilitated by years of fiscal neglect, frantically bought up the first Airacorbras. In 1940, the French and the British each signed contracts for hundreds of export Airacobras. The order came too late for the French and the British found nothing to like in the P-39 so many of these airplanes were redirected to the Air Corps and redesignated as P-400s. The British Government sent most its P-39s to the Soviet Union. The Army Air Corps had absorbed 179 Airacobras destined for England and most of these fighters went into action in the Pacific Theater with the 8th Pursuit Group at Port Moresby, New Guinea, in April 1942. For the next year-and-a-half, the best fighter aircaft the United States could field were P-39s and Curtiss P-40s.

The Museum's Airacobra, a P-39Q-15BE, serial no. 44-2433, saw no combat during World War II. Bell manufactured it at Buffalo and delivered it to the USAAF on November 14, 1943. The airplane was initially assigned to the 369th Fighter Group, a replacement training unit, at Hamilton Field, California. It served at three airfields (Moses Lake, Paine Field, and McChord) in Washington state between August 30 and November 29, 1944. Then it was delivered to a War Assets Administration depot in Ponca City, Oklahoma, for disposal, and the U. S. Army Air Forces dropped it from the inventory on December 6, 1944.

After the war, P. J. "Sep" Mighton of Tulsa, Oklahoma teamed with Earl Ortman and bought the P-39 to compete in the National Air Races held at Cleveland, Ohio. Ortman was already famous for his air racing exploits before the war but he wanted to fly a North American P-51 Mustang in the Thompson Trophy event. Ortman and Mighton hired Charles W. Bing to race the P-39 on August 31, 1946, in the Sohio Trophy event. Bing flew the fighter to 7th and last place. Ortman and Mighton should have expected the Aircobra's poor showing because most of the field flew much faster airplanes such as the North American P-51 Mustang.

Elizabeth Haas then bought the airplane and registered it with the FAA as NX57591 on December 4, 1946. The airplane wore her red and white racing colors and the nickname "Galloping Gertie" painted on the fuselage side. She took it back to the National Air Races in 1948 but failed to qualify. Haas lent her P-39 to the National Air Museum in 1950, but a lack of space forced the Museum to store it temporarily at Orchard Place Airport (now O'Hare International Airport) near Chicago, Illinois. In 1956, Ms. Haas made the donation permanent. After NASM lent the Airacobra to the Experimental Aircraft Association (EAA) Museum at Oshkosh, Wisconsin, the EAA repainted it in U. S. Army Air Force markings but kept the nickname "Galloping Gertie." EAA returned the aircraft to the National Air and Space Museum in 1984. Since 1999, the P-39 has been on loan to the Niagra Aerospace Museum, Niagra Falls, New York.