Gun Sight Dimmer Switch, Mark 21, for Mark 18 Gun Sight US Navy Lockheed The {Gentex} H-4 was a

The {Gentex} H-4 was a further development of H-3

The type of aircraft which used this tachometer has not yet been identified by us

The SCR 269 system (see diagram)

part number 1556-2K-A

WWII-era US Navy Douglas SBC Dive Bombers as well as early 'birdcage' versions of the Vought F4U-1 Corsair Fighter

Gun Sight Dimmer Switch, Mark 21, for Mark 18 Gun Sight US Navy Lockheed The {Gentex} H-4 was aThis Dimmer Switch Box was a component of the Mark 18 Gun Sights used in late WWII and Korean War era US Navy fighters and bomber turrets. This unit adjust the illumination of the projected reticle in sight as needed. See instructions for use from the 1945 USN Aircrew Gunnery Manual in the photo gallery. It is in exceptional condition given its age. The dial markings are clear and the glass and case are intact. Measures ~2. 25 inches diameter and ~3