The Republic-Ford JB-2, also known as the Thunderbug, KGW and LTV-N-2 Loon, was an American copy of the German V-1 flying bomb. Developed in 1944, and planned to be used in the Allied 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, roughly 120 kilometers (75 miles) northeast of the V-1 test launch ramp at the Peenemünde Army Research Center, on Germany's Usedom Island. 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 the airfield at 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
As more intelligence data was obtained through aerial photography and sources inside Germany, the United States decided to develop a jet-powered flying bomb in 1943. 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.
Motivated by intelligence information supplied by the United Kingdom, Project MX-544 was initiated to create an American copy of the V-1. In July 1944, three weeks after German V-1 "Buzz Bombs" first struck England on 12 and 13 June, 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. The matter of guided missiles became a jurisdictional issue between Army ground Forces and the Army Air Forces. The dispute was decided in favor of the AAF as the JB-2 had wings and flew. It was decided that the JB-2 "should be placed in combat, needed or not, as an insurance measure for AAF claims.Rosenberg 1964 p. 19.
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 only slightly in dimensions. The wing span was only wider and the length was extended less than . The difference gave the JB-2 of wing area versus 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. A similar, completely coincidental re-shaping, but with a much broader chord, was used for the same airframe componentSideview of a preserved Fi 103R, with similar-shape, broader-chord forward pulsejet pylon to that of the JB-2 of the manned Fieseler Fi 103R Reichenberg, original V-1 ordnance development. Initial testing of the first batch of prototype missiles resulted in a decision to change from the preset guidance of the V-1 to a command guidance system utilizing a radar beacon in the missile and radio command guidance from a tracking SCR-584 radar.Werrell 1972 p. 65
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. Early launches of JB-1, JB-2, and JB-10 missiles were from a site along the coast on Santa Rosa Island in what is now Sandestin, Florida. The land necessary was leased at $1 a year for the duration of the war. The test location was east of Eglin Army Air Field designated Range 64 (aka C-64) () and involved of the island’s shore line as well as extending off shore. Range 64 was a self-sufficient facility with not only launch and missile preparation facilities, but included barracks, mess hall and administrative facilities as well. Later a Training Unit P had to be located east of Range 64 to house men developing the techniques needed for field operations in combat while being trained to field the JB-2. Ultimately nine launch ramps of varying length and method of propulsion were built at Range 64. While copying the V-1 proved easy, inventing a means of launching proved very difficult. The first launch of a JB-2 from Range 64 was on October 12, 1944 by the 1st Proving Ground Group. A total of 233 JB-2s were launched from Range 64 between October 1944 and October 1945. All further tests at Range 64 were cancelled in November 1945 and orders were issued to deconstruct, remove or abandon everything by December 12, 1945. After the war ended the land leased for a single dollar was returned to the Coffeen family. The site of Range 64 is now the Coffeen Nature Preserve, Four Mile Village and Topsail Hill Preserve State Park in Sandestin, FL.
As the Heinkel He 111H-22 had done late in the war for the Luftwaffe in offensive air-launches of V-1s against the Allies, JB-2s were launched from MB-17G 44-85815 based at Hurlburt Field beginning in early 1945 and continued after the war ended.
In addition to Range 64, a detachment of the Special Weapons Branch, Wright Field, Ohio, arrived at Wendover Field, Utah, in 1944 with the mission of evaluating captured and experimental systems, including the JB-2. Testing was from a launch structure just south of Wendover's technical site. Unlike the missiles fired at Range 64 the ones fired at Wendover were armed and fired in the direction of a distant mountain range where their destruction by ground impact was assured. 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 from Range 64. 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 Company built the engine, initially designated IJ-15-1, which was a copy of the V-1's 900-lb. thrust Argus-Schmidt pulse-jet (the Argus As 014), 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.
Development of an improved guidance method for the JB-2 began in 1945. By April the Aircraft Radio Laboratory at Wright Field had developed a radio/radar control system utilizing the highly accurate SCR-584 radar unit to track a AN/APW-1 radar transceiver equipped JB-2. A SCR-584 tracked the missile's transceiver and sent control signals to correct the missile's course. With the new guidance system the JB-2 became a much more advanced missile than the V-1.
At one point proponents envisioned 75,000 JB-2s planned for production. This was absurd as it would have competed with the established manned bomber forces for sealift from America to Europe. It was estimated that the presumed launch rate of JB-2s would consume 25% of available shipping. Commander of Strategic Air Forces in Europe, Spaatz proposed a much more limited role as a harassment weapon on days where weather limited bombers. Moreover the air forces only wanted the JB-2 if it caused no curtailment of the supply of bombs, artillery shells, and personnel being shipped to Europe.Werrell 1972 p. 64 A USAAF launching squadron was formed in anticipation for using the weapons both against Nazi Germany and Japan. The motive for this rush to deploy the JB-2 was the struggle for control of guided missiles between the Army Air Force and the Army Ground Forces. This was the opening round of a struggle between the Army and Air Force over the guided missile which would last until the late 1950s. 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. 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. Deployment of the JB-2 from the ground would require their deployment after landings had been accomplished. Deployment from B-29s would take too long to modify the B-29s necessary. 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. As WWII ended in Europe the Army Air Forces had JB-2 crews on transports headed for use against Japan.Werrell 1972 p. 91 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 were manufactured.
Postwar testing Though production was halted in mid-September 1945 testing was continued with JB-2s already constructed.Rosenberg 1985 p. 38. Planning for the post war development of Guided Missiles at Eglin had begun prior to VJ Day. On August 13, 1945 a stretch of Santa Rosa Island was purchased by the USAAF for the launch of guided missiles. The replacement launch site was located 22 miles further west on Santa Rosa island from Range 64. Following the war the 1st Experimental Guided Missiles Group was created in January 1946 to replace the ad hoc units which had been at Range 64.