Aircraft Recognition Manual FM30-30 War Department 1943 C-119 It was used in conjunction

It was used in conjunction with suitable beacons for night landing of parachute troops

and AC US ARMY are imprinted on its face

While it resembles a flap indicator

it is fair to assume that this would have been installed in either the Douglas A-20 Havoc or A-26 Invader

The knob rotates the compass card when pushed in and turned

Aircraft Recognition Manual FM30-30 War Department 1943 C-119 It was used in conjunctionThis manual was standard issue to air crew during WWII by both the US Army Air Force and US Navy. It educates the reader on the general visual methods of aircraft recognition in the first section, then provides specific recognition cues for key aircraft of the US, its Allies, and the Axis nations. The manual contains the most commonly encountered aircraft in each theater, as well as a few more esoteric ones. Few have survived in this condition. Nearly