The USAAF refused to give Republic any money for the development of the new XP-47B, so Republic paid for the construction of the first mock-up, reusing the cockpit area of the P-43. By the time the prototype was ready for testing, it weighed over 12,550 lb, over the Army's limit for the new fighter design, and far more than any single-engine fighter ever developed. It also could carry only 298 gallons of fuel, 17 gallons less than the requirement, but the Army was generally pleased with its performance, achieving speeds of at , and overlooked these issues.