History
Design and Development
The development of the Fisher P-75 fighter began in September 1942, when the Fisher Body Division of General Motors responded to a US Army Air Forces requirement for a high-performance interceptor with exceptional climb capability. At the time, GM was providing manufacturing support for Grumman aircraft, and Fisher Body, best known for its automotive background and production of Sherman tanks, aimed to contribute to the war effort with an original aircraft powered by the ambitious Allison V-3420 engine.
Lacking experience in aviation design, Fisher recruited Donovan R. Berlin, the renowned Curtiss designer responsible for the P-36 and P-40. In September 1942, Berlin’s team submitted a proposal for a large, single-seat fighter that combined major components from existing aircraft: inverted gull wing panels from the P-51 Mustang, a tail assembly from the Douglas SBD Dauntless, landing gear from the Vought F4U Corsair, and a layout inspired by the Bell P-39 Airacobra, with the engine mounted behind the cockpit. Contra-rotating propellers were driven via long extension shafts. The armament would consist of four .50 caliber machine guns with 300 rounds per gun in the nose and six additional guns in the wings, each with 235 rounds, plus underwing hardpoints for two 500-pound bombs. By reusing proven components, Fisher hoped to accelerate development and achieve production readiness within six months.
After reviewing the proposal, the Army awarded a contract in October 1942 for two XP-75 prototypes, with delivery of the first aircraft expected by May 1943. The XP-75 would be the first aircraft to use the complex V-3420 engine, rated at 2,600 horsepower and mounted centrally in the fuselage. Performance estimates projected a top speed of 440 mph at 20,000 feet, a climb rate of 5,600 feet per minute, and a service ceiling of 38,000 feet. During the early design phase, P-40E Warhawk wing panels were temporarily substituted for the intended P-51 components.
In the spring of 1943, the initial mockup underwent inspection, retaining the P-40 wings. As the design matured, strategic priorities shifted. By the summer of 1943, the Army’s focus had moved toward long-range escort fighters rather than interceptors. Consequently, the program was modified to include six XP-75A aircraft with increased internal fuel capacity and upgraded 2,885 hp V-3420-23 engines intended for extended-range missions. A definitive production contract was signed on October 1, 1943. By the end of September 1943, only the first two XP-75s were complete, and the first XP-75A configured for escort missions followed in December. That July, the Army had issued a letter of intent for 2,500 production P-75A aircraft, pending successful test performance.
Flight Trials
The first two XP-75 prototypes were assembled in Detroit, while all subsequent aircraft were slated for production at Fisher’s plant in Cleveland, Ohio. The XP-75 flew for the first time on November 17, 1943, followed soon after by the second prototype. Test flights quickly revealed serious design flaws. The aircraft exhibited longitudinal instability caused by a miscalculated center of gravity, excessive aileron forces at high speeds that hampered roll performance, and unpredictable spin recovery. Engine problems further complicated testing, including power loss and inadequate cooling. With production deadlines looming, Fisher’s engineers had to implement urgent modifications.
A series of improvements were introduced into the XP-75As to address these issues. The ailerons were enlarged and fitted with hydraulic assistance, improving roll response. The tail received a dorsal extension and a small ventral fin to enhance spin stability. The canopy was replaced with a bubble design to improve visibility, and the nose was lengthened to rebalance the center of gravity. These and other adjustments were incorporated in time for the production of the first P-75A airframe.
The first XP-75A flew in February 1944, but the program suffered a tragedy on April 8 when the third aircraft (serial 44-32163) crashed, likely due to unauthorized low-altitude aerobatics, killing the pilot. Despite this tragedy, testing continued, though the Army’s reliance on existing long-range fighters like the P-38, P-47, and P-51 had by then rendered the P-75 less relevant. Engineering revisions also caused significant cost overruns, leading the Army to reduce its order to just 25 production aircraft.
Performance trials resumed in June 1944. One aircraft, XP-75A serial 44-32161, reached 418 mph at 21,600 feet and a climb rate of 2,990 feet per minute. Still, its engine was likely underperforming at just 2,210 horsepower, and the aircraft’s empty weight had increased by over 1,300 pounds, adversely affecting its flight characteristics.
The first production P-75A was rolled out on September 15, 1944, and began flight testing soon after. It featured redesigned tail surfaces, blunt wingtips, new ailerons, a ventral fin, and a bubble canopy, many of the improvements already tested on the XP-75As. Two more production aircraft were sent to Eglin Field for tactical suitability trials. On October 10, one of these aircraft (serial 44-44549) crashed during testing, killing the pilot. Further speed trials showed that the aircraft failed to meet guaranteed performance by as much as 30 mph. An experimental intercooler was installed on aircraft 44-44551 to improve power output, but by then it was too late to influence the Army’s decision.
Recognizing that the P-38, P-47, and P-51 already exceeded operational needs, the Army canceled all further P-75A production on October 6, 1944. The cancellation capped the program at 20 aircraft, of which only five were completed (serials 44-44549 through 44-44553), and a sixth (44-44554) was delivered in incomplete condition to be used as a spare kit. The completed aircraft were relegated to experimental work, including drag reduction and propeller tests, before the program was terminated on November 8, 1944.
Following Japan’s surrender, most remaining P-75s were scrapped. One aircraft, 44-44551, was retained by Allison for engine tests but was never flown. The final completed P-75A, serial 44-44553, survived and is now preserved in non-flying condition at the National Museum of the United States Air Force in Dayton, Ohio. It underwent a full restoration in 2008. In total, Fisher produced two XP-75s, six XP-75As, and six P-75As.
Epilogue
Although the Fisher P-75A program ended in a cancellation, it represented a determined effort by a company with no prior experience in aircraft design. The engineers at Fisher faced development challenges and shifting military requirements, yet they made rapid progress compared to many other experimental designs by reputable aeronautical firms. Despite its flaws, the P-75 was a bold attempt to create a powerful, quickly produced interceptor using innovative construction methods and parts commonality. Had the original requirement for a fast-climbing fighter remained unchanged, the P-75A might have seen limited production and service during World War II. Thus, ultimately, the P-75A was Fisher’s first and last aircraft designed and assembled.
