This restricted U.S. Army Air Force film from WWII (probably 1944) educates viewers on the electrical operation of the Central Station Fire-Control System. This was a mechanism produced by General Electric for the Boeing B-29 Superfortress. It allowed the gun turret and the gunner’s sighting station to be located separately, in efficient positions for each, yet still maintain alignment between the sight and the gun itself. This was used in the Boeing B-29 Superfortress which was a four-engined bomber employed by the United States Army Air Forces during World War II and the Korean War. The aircraft had four remotely controlled turrets, each with two machine guns. These were connected via the Central Station Fire-Control Systems to the sighting stations.

(00:09) AF-146 Produced for and Approved by Army Air Forces. Presented by General Electric.

(00:23) The Central Station Fire-Control System & Electrical Operation

(00:33) Animation of a Boeing B-29, the sole plane to use the Central Station Fire-Control System produced by General Electric.

(00:41) This system had many advantages such as allowing an effective placement for both the gun turret and the sighting station. They are placed apart from each other and the electric control causes the gun to automatically follow the gunner’s line of sight.

(01:03) A diagram of the electric circuit with labels for each element of the circuit: the sighting station, the turret, the servo-amplifier, the dynamotor, the amplidyne generators, and the engine.

(01:40) Drawing of the amplidyne generator which is driven by a motor and a current is produced in the armature.

(03:08) The alternating voltage, through the Selsyn transmitter and Selsyn receiver enables the alignment of the sight and the gun.

(05:46) Diagram of a Servo-amplifier channel containing the power supply transformer, the signal input transformer, and two vacuum tubes.

(06:09) Three main elements of a vacuum tube: the plate, control grid, and cathode. The tube can operate as an open or closed switch.

(07:26) Overview of how the tubes are connected into the system.

(10:07) A flow of current produces a DC voltage in the amplidyne generator which sends a current to the turret, aligning it with the sight.

(10:45) Cut-away shot of the B-29 with a crewman operating the sight. He moves the sight above the gun.

(11:06) Diagram showing the resulting effects on the electrical grid, causing the turret to rotate in the opposite direction and move into alignment.

(13:10) Cut-away footage of the B-29, showing a gun turret that moves unstably.

(13:56) The diagram shows how this is eliminated by a mechanism that causes the turret to slow down its movement when close to alignment.

(14:38) Animation of a stabilized current.

(15:01) Footage of the gun and sight traveling in alignment.

(16:40) Diagram of the 31-speed and the 1-speed. The 1-speed units take control when the misalignment is significant.

(17:14) A man points to the signal input transformer, the double vacuum tube, condenser, output transformer, and two neon lamps. These parts and the 1-speed are wired into a circuit.

(17:52) Diagram of how this circuit is applied to the system.

(19:39) Video of the gunner moving the sight with the power off, the turret does not follow the sight.

(19:48) Diagram of the electrical grid shows how when the power is then turned on, the 1-speed controls until the 31-speed takes care of the final alignment.

(21:02) Footage of the servo-amplifier

(21:29) Animation of the turret following the sight.

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