Aircraft Clock, 8-day, Type A-9, Air Corp US Army 1940

This is a mechanical WWII-era aircraft clock, Type A-9, that was used across nearly all aircraft of the US Air Corps and Air Force, including bombers B-17, B-24, B-25, and fighters P-38, P-40, P-47, and P-51. 

The time is set by pulling out and rotating the knob at the front left corner and rotating. The clock is wound by rotating the same knob.  The knob in the upper right corner is a light receptacle for a small bulb, not included, which would be turned to illuminate the clock.  This example has a serial number prefix of AC-40, indicative of a year of manufacture of 1940. The clock winds but does not continue to run. Measures ~2.25 square and ~1.25 inches deep.