Gun Sight Dimmer Switch, Mark 21, for Mark 18 Gun Sight US Navy
This 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 inches deep. See photos.