Gun Sight, Reflector, Mk IIIA 7A/1313 RAF RCAF GJ3 A4 Skyhawk "Bureau of Aeronatics" of the

"Bureau of Aeronatics" of the US Navy is engraved on its face and on back

such as heavy bombers B-17 and B-24

Here's a bit of history from the Rochester Avionics Archive:

The pointer indicates altitude from 0-20

Gun Sight, Reflector, Mk IIIA 7A/1313 RAF RCAF GJ3 A4 Skyhawk "Bureau of Aeronatics" of theHere is a fine example of the Reflector Gun Sight Mk IIIA, 7A 1313. The Mk IIIA, aka Barr & Stroud model GJ3, was adopted by the RAF as the standard turret and free gun sight for their aircraft. The Mk IIIA consisted of a detachable lamp unit and an upright sight head. The lamp unit is removed by depressing a small button on the bottom of the housing, revealing the bulb and circuitry. The brightness of the bulb was adjusted by the gunner by rotating