Reverse Engineering and America's First Practical Cruise Missile

On June 12, 1944 Germany's first Vergeltungswaffe or "reprisal weapon" was inaugurated into active service. The V-1 flying bomb - or cruise missile, in the parlance of our times - would continue to rain on Allied territory (primarily London) until March 12, 1945. A total of nearly 30,000 V-1's had been manufactured during the course of the war; of these, roughly 10,000 were launched towards England. The guidance system on the V-1 was primitive, to say the least: the missiles were fueled based on the number of kilometers from launch to target divided by estimated fuel economy. With luck, the V-1 ran out of gas just over its target, entered a steep dive, and crashed into an urban building, causing great chaos and confusion. Fueling the V-1, however, was not an exact science; nor was quality control particularly stellar - by some estimates 1 in 4 of the missiles failed to reach their targets due to manufacturing oversight or guidance error. Both factors resulted in a handful of V-1's crash-landing without detonating their warheads, and by July of 1944 - only a month after the weapon's first operational flight - enough information had been gleaned from crashed V-1's that the United States Army decided to build some of their own. The result would be the JB-2 Loon Jet Bomb.

Reverse engineering proceeded quickly, with the USAAF producing, at Wright Field, a limited number of missiles for testing at Eglin Field in Florida. In October 1944 the JB-2 underwent its first successful test flight. That same month a contract for production was signed with Republic Aviation Corporation and the Ford Motor Company. Republic would manufacture missile airframes while Ford was responsible for construction of the pulsejet. Republic would eventually subcontract most of the airframe production to Willys-Overland, a firm which today is better known for designing the Jeep.

Although essentially a recreation of Germany's V-1 the JB-2 differed from its predecessor in two important ways. The first of these is the missile launch mechanism. A pulsejet must be traveling at greater than 200 mph before the engine will engage; the V-1 achieved this speed by being launched from a steam-powered catapult, a system similar to the one used today on many aircraft carriers. USAAF designers opted instead to achieve launch velocity though Jet Assisted Take Off, whereby a pair of solid rocket boosters, attached to either side of the JB-2's fuselage, propelled the missile down a ramp until a launch speed of 220 mph was reached and pulsejet propulsion took over. A number of tests also demonstrated that the B-17 Bomber could be employed as a launch platform, a technique pioneered by the Germans with the V-1. The second difference between the V-1 and the JB-2 lay in the guidance system. The USAAF, recognizing the inherent drawbacks of the original V-1 guidance package, began testing a radio guidance package in early 1945. JB-2's were fitted with a radio transmitter, which could be tracked by ground-based receivers and used to determine the missile's location, altitude, and velocity. A guidance control package on the missile allowed a remote operator to signal course corrections and initiate the terminal dive. Although much more accurate than the system used on the V-1 and the original JB-2, this modified version still fell an average of 400 meters off-target when tested under ideal conditions.

Development of the JB-2 was undertaken primarily by the US Army; even so, the Navy had shown interest in the program from the start. In preparation for the planned invasion of Japan the two agencies placed orders for the flying bomb to the tune of 12,000 units; the invasion never materialized, and all orders were cancelled after VJ-Day. Although the missile never saw use in combat a number of JB-2s were being readied for deployment aboard an escort carrier as the war came to a close; these naval versions were identical to those produced for the Army.

After the war the Loon was used primarily as a test vehicle for research into a more advanced generation of guided missile technology. The Army Air Force designation for these launch test vehicles was LTV-1; after the National Security Act of 1947 created a separate Department of the Air Force in 1947 this same test vehicle was designated LTV-A-1. The Army and Air Force discontinued use of the Loon for flight tests in 1949. The Navy did not deploy the JB-2 after the war, although in late 1945 it was proposed that a re-designated JB-2 (KGW-1; they retained the service nickname Loon) be deployed as a submarine-launched version of the weapon. First flight of the KGW-1 occurred in January 1946. That March funds were set aside to convert two submarines to carry the Loon and its associated guidance equipment. The naval Loon soon followed its Army cousin and was relegated to the status of a testing and research vehicle. As such it was again re-designated, this time as the KUW-1. It was under this moniker that the Loon was tested as the first submarine launched cruise missile in the early months of 1947, with the first successful test being that March. That September the Loon was used for further feasibility testing of naval guided missile technology and was once re-designated, becoming the LTV-2. The final iteration of the Loon came in early 1948, when it received its final re-designation as the LTV-N-2. The LTV-N-2 program was axed in March of 1950, with the results of that being used in development of the Regulus cruise missile.

Vital Statistics
Warhead: One 2,100 lb. High-Explosive Warhead
Range: 150 miles
Wingspan: 17 ft. 8 in.
Length: 27 ft. 1 in.
Weight: 5,023 lbs. (fully loaded)
Propulsion: One Ford PJ-31-F1 Pulsejet (generating 900 lbs. of thrust); this engine was essentially a copy of the V-1's Argus pulsejet.
Cruise Speed: 375-400 mph
Launch Speed: 220 mph
Guidance: Radio course and dive control; the initial design retained the V-1's primitive fire-and-forget guidance system.
Other Army Designations: LTV-1
Other Air Force Designations: LTV-A-1
Other Navy Designations: KGW-1; KUW-1; LTV-2; LTV-N-2

Sources:
Federation of American Scientists
National Museum of the United States Air Force
Encyclopedia Astronautica