2,500-pound GB-4 Air-to-Surface Missile

Over-all length

Wing span, feet

Over-all height

Diameter of body, inches

Total weight, pounds

Warhead

Fuzing

Nose - AN-M103, M139, or M140
Tail - T59

General: GB-4 is a glide bomb which is launched from an aircraft and guided by re-mote radio control to its surface target by employing television intelligence picked up by a television camera on the missile and radioed to a receiver in the launching plane. It has a special plywood airframe built around a 2,000-pound bomb, with rudders and elevators but no ailerons. The air-frame is fastened to a magnesium casting threaded to the tail of the bomb.

The missile is effective against well defined point targets, easily distinguishable from the surroundings on a television screen, and has an average circular error of 200 feet. At present, the weapon can be used only under good visual bombing conditions, but it has been proposed to incorporate radar tracking of the missile by the parent aircraft to alle-viate the handicap.

It is launched outside the normal antiaircraft range from either a B-17 or B-25 at 175 m.p.h. at a preferred distance of 17 miles from the target at an altitude below 15,000 feet. With a glide ratio of 6 to 1, the time of flight, at average rates of 250 to 300 m.ph., is four minutes.

Control: The television camera mounted under the bomb is set to point along the bomb's flight path, the standard setting being 3° below the axis of the bomb. The field of view is 14° wide and 18° high. The camera scans the area and modulates a transmitter with the picture which is broadcast to the parent aircraft. The radio control signals are transmitted by a "liaison" transmitter in the parent plane and are received by a standard or command set receiver installed in the glide bomb. A modulator installed in the airplane will put out any one of five audio tones to modulate the transmitter. The relays in the control unit switch current to the elevator servo motor and the rudder capstan motor to move the control surfaces in the desired directions. In addition, two more relays are ac-tuated to shift temporarily the gyro pick-offs either to the right or to the left when those signals are given. The missile is stabilized by a directional gyro to give roll and azimuth control.

Suspension: The missile is carried outside the plane on a Shackle D7. Electrical cab-les, connected to it, pull out on release.

Destructor: The Destructor T9 is placed in the control box and is actuated, on im-pact, by the Fuze T62.

Figure 389. GB-4 Missile