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The Republic-Ford JB-2, also known as the KGW and LTV-N-2 Loon, was a United States copy of the German V-1 flying bomb. Developed in 1944, and planned to be used in the United States invasion of Japan (Operation Downfall), the JB-2 was never used in combat. It was the most successful of the United States Army Air Forces Jet Bomb (JB) projects (JB-1 through JB-10) during World War II. Postwar, the JB-2 played a significant role in the development of more advanced surface-to-surface tactical missile systems such as the MGM-1 Matador and later MGM-13 Mace. ==Wartime development== The United States had known of the existence of a new German secret weapon since 22 August 1942 when a Danish Naval Officer discovered an early test version of the V-1 that had crashed on the island of Bornholm, in the Baltic Sea between Germany and Sweden. A photograph and a detailed sketch of the V-1 test unit, the Fieseler Fi 103 V83 (''Versuchs''-83, the eighty-third prototype airframe) was sent to Britain. This led to months of intelligence-gathering and intelligence-sifting which traced the weapon to Peenemünde, on Germany's Baltic Coast, the top-secret German missile test and development site.〔U.S. Air Force Tactical Missiles, (2009), George Mindling, Robert Bolton ISBN 978-0-557-00029-6〕 As more intelligence data was obtained through aerial photography and sources inside Germany, it was decided in 1943 for the United States to develop a jet-powered bomb as well. The United States Army Air Forces gave Northrop Aircraft a contract in July 1944 to develop the JB-1 (Jet Bomb 1) turbojet-powered flying bomb under project MX-543. Northrop designed a flying-wing aircraft with two General Electric B1 turbojets in the center section, and two 900 kg (2000 lb) general purpose bombs in enclosed "bomb containers" in the wing roots. To test the aerodynamics of the design, one JB-1 was completed as a manned unpowered glider, which was first flown in August 1944.〔 However, in July 1944, three weeks after German V-1 "Buzz Bombs" first struck England on June 12 and 13, American engineers at Wright Field, fired a working copy of the German Argus As 014 pulse-jet engine, "reverse-engineered" from crashed German V-1s that were brought to the United States from England for analysis. The reverse engineering provided the design of America's first mass-produced guided missile, the JB-2.〔(USAFHRA document 01014091 )〕 By 8 September, the first of thirteen complete JB-2s, reverse engineered from the material received at Wright Field in July was assembled at Republic Aviation. The United States JB-2 was different from the German V-1 in only the smallest of dimensions. The wing chord was only 2½ inches wider and the wingspan was extended less than . The difference gave the JB-2 60.7 square feet of wing area versus 55 for the V-1.〔 One of the few visible differences between the JB-2 and the V-1 was the shape of the forward pulsejet support pylon — the original V-1 had its support pylon slightly swept back at nearly the same angle on both its leading and trailing edges, while the JB-2's pylon had a vertical leading edge and sharply swept-forward trailing edge. With its Ford-produced PJ31 pulsejet powerplant, the JB-2 was one of the first attempts at a powered cruise missile for potential usage in America's arsenal. The JB-2 had nothing more advanced than what the Germans had already placed aboard their V-1 for guidance, while the indigenously designed, unpowered U.S. Navy's ''Bat'' anti-ship missile already had an active radar homing system in its nose to locate its intended maritime targets. The first launch of a JB-2 took place at Eglin Army Air Field in Florida by the 1st Proving Ground Group on 12 October 1944. In addition to the Eglin group, a detachment of the Special Weapons Branch, Wright Field, Ohio, arrived at Wendover Field, Utah, in 1944 with the mission of evaluating captured & experimental systems, including the JB-2. Testing was from a launch structure just south of Wendover's technical site. The launch area is visible in aerial imagery (). Parts of crashed JB-2s are occasionally found by Wendover Airport personnel.〔 In December 1944, the first JB-1 was ready for launch. The missile was launched by a rocket-propelled sled along a 150 m (500 ft) long track, but seconds after release the JB-1 pitched up into a stall and crashed. This was caused by an incorrectly calculated elevon setting for take-off, but the JB-1 program was subsequently stopped, mainly because the performance and reliability of the GE B1 turbojet engines were far below expectations. In addition, the cost to produce the Ford copy of the Argus pulse-jet engine of the JB-2 was much less than the GE turbojets. Subsequently work proceeded on the JB-2 for final development and production.〔〔Garry R. Pape, John M. Campbell: "Northrop Flying Wings", Schiffer Publishing Ltd., 1995〕 An initial production order was 1,000 units, with subsequent production of 1,000 per month. That figure was not anticipated to be attainable until April 1945. Republic had its production lines at capacity for producing P-47 Thunderbolts, so it sub-contracted airframe manufacturing to Willys-Overland. Ford Motor Co built the engine, initially designated IJ-15-1, which was a copy of the V-1's 900-lb. thrust Argus-Schmidt pulse-jet, later designated the PJ31. Guidance and flight controls were manufactured by Jack and Heintz Company of Cleveland, Ohio, and Monsanto took on the task of designing a better launching system, with Northrop supplying the launch sleds. Production delivery began in January 1945.〔 An envisioned 75,000 JB-2s were planned for production. A USAAF launching squadron was formed in anticipation for using the weapons both against Nazi Germany and Japan. However, the end of the European War in May 1945 meant a reduction of the number of JB-2s to be produced, but not the end of the program. Army commanders in Europe had dismissed it as a weapon against Nazi Germany, as the strategic bombing concept was implemented and by 1945 the number of strategic targets in Germany was becoming limited. However, the JB-2 was envisioned as a weapon to attack Japan. A 180-day massive bombardment of the Japanese Home Islands was being planned prior to the amphibious landing "by the most powerful and sustained pre-invasion bombardment of the war". Included in the assault were the usual naval bombardment and air strikes augmented by rocket-firing aircraft and JB-2s.〔 A navalized version, designated KGW-1, was planned to be used against Japan from LSTs (Landing Ship, Tank) as well as escort carriers (CVEs). In addition, launches from PB4Y-2 Privateers were foreseen and techniques developed. The official U.S. Air Force Fact Sheet on the JB-2 states just before the end of the war, an aircraft carrier ''en route'' to the Pacific took on a load of JB-2s for possible use in the planned invasion of the Japanese home islands, however the name of the carrier has never been identified. In addition, according to one Eglin AFB history, an unidentified USAAF unit in the Philippines was preparing to launch JB-2s against Japan.〔 The war's end led to the cancellation of Operation Downfall and the production of JB-2s was terminated on 15 September. A total of 1,391 units were manufactured.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Republic-Ford JB-2」の詳細全文を読む スポンサード リンク
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