JB-4

The JB-4, also known as MX-607, was an early American air-to-surface missile developed by the United States Army Air Forces during World War II. Using television/radio-command guidance, the JB-4 reached the flight-testing stage before being cancelled at the end of the war.

Design and development
Developed under the project code MX-607 at Wright Field in Ohio, the JB-4 was a modification of the GB-4 glide bomb, which had entered service with the U.S. Army Air Forces in 1944. Powered by a Ford PJ31 pulsejet engine, the JB-4 was intended to give an improved standoff range as opposed to its unpowered predecessor. In addition, the addition of an engine made the missile capable of being ground-launched as well. However the requirement to carry fuel for the engine meant that the size of the JB-4's warhead was limited to 750 lb, compared to the 2000 lb bomb that formed the core of the GB-4.

Utilising primarily plywood construction, the JB-4 utilised television/radio-command guidance, with an AN/AXT-2 transmitter broadcasting a television signal from a camera in the missile's nose to a remote operator. The operator, viewing the transmitted picture, would then transmit commands to the missile via radio, correcting the missile's course to ensure striking the target.

Operational history
The JB-4 entered the flight testing stage in January 1945. The missile demonstrated the ability to cruise at over 400 mph; however, the television-guidance concept suffered from the limitations of the technology of the time, the pictures being difficult to make out in anything except completely clear weather. The missile also suffered from reliability issues; these, combined with the end of World War II in August 1945, resulted in the termination of the project, with none of the JB-4s built seeing operational service.