On November 11, 1944, Republic received an order for three prototypes of the new XP-84. Since the design promised superior performance to the P-80 Shooting Star and Republic had extensive experience in building single-seat fighters, no competition was held for the contract. The name Thunderjet was chosen to continue the Republic Aviation tradition started with the P-47 while emphasizing the new method of propulsion. On January 4, 1945, even before the aircraft took to the air, the USAAF expanded its order to 25 service test YP-84A and 75 production P-84B (later modified to 15 YP-84A and 85 P-84B). Meanwhile, wind tunnel testing by the National Advisory Committee for Aeronautics revealed longitudinal instability and buckling of stabilizer skin at high speeds. The weight of the aircraft, a great concern given the low thrust of early turbojets, was growing so quickly that the USAAF had to set a gross weight limit of 13,400 pounds (6,078 kg). The results of preliminary testing were incorporated into the third prototype, designated XP-84A, which was also fitted with a more powerful J35-GE-15 engine with 4,000 pound-force (17.80 kN) of thrust.