| JB-4 | |
| Origin: | United States |
| Type: | Air-to-surface missile |
| Is Missile: | yes |
| Service: | 1945 |
| Used By: | United States Army Air Forces |
| Filling: | High explosive |
| Filling Weight: | bomb |
| Engine: | Ford PJ31 pulsejet |
| Engine Power: | 660lb-f |
| Speed: | 445mph |
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.
Developed under the project code MX-607 at Wright Field in Ohio,[1] the JB-4 was a modification of the GB-4 glide bomb,[2] which had entered service with the U.S. Army Air Forces in 1944.[3] Powered by a Ford PJ31 pulsejet engine, the JB-4 was intended to give an improved standoff range as opposed to its unpowered predecessor.[2] In addition, the addition of an engine made the missile capable of being ground-launched as well.[2] However the requirement to carry fuel for the engine meant that the size of the JB-4's warhead was limited to, compared to the bomb that formed the core of the GB-4.[4]
Utilising primarily plywood construction,[5] 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.[2]
The JB-4 entered the flight testing stage in January 1945.[2] [6] The missile demonstrated the ability to cruise at over ;[7] 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.[3] 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,[2] with none of the JB-4s built seeing operational service.[8]