Lack of fighter escorts for B-29s was a concern for the USAAF as their missions approached mainland Japan. One idea was to have fighters launched from aircraft carriers located closer to Japan protect the bombers during the bombing raid. At that time no US Navy fighters had enough range to support the mission. The North American P-51 Mustang had become the premier long-range escort fighter by late 1943, but was not designed for carrier-based operations. A classified program “Project Seahorse” was approved and P-51D-5-NA, serial number 44-14017, was retained by North American Aviation in Dallas, Texas for modifications to create a navalized version of the P-51. Aerodynamic, structural and landing gear changes were incorporated and the aircraft was redesignated as the ETF-51D. After two months of testing at Mustin Field, PA the ETF-51D was transferred to the USS Shangri-La (CV-38) Essex class carrier undergoing a shakedown cruise off the coast of Virginia. Navy Lieutenant Robert Elder made the first P-51 carrier landing on November 15, 1943. The carrier suitability trials ended after only 25 landings and launches were made. The airfields on the islands of Okinawa and Iwo Jima were taken over by US forces in early 1945, providing fighter units with forward bases to escort the bombers to mainland Japan. Thus a navalized P-51 was no longer required and the program was terminated.