Aircraft Clock, Elapsed Time USAF USN MS28020LI
This is an original Cold War-era Elapsed Time Clock, made for US military aircraft applications by Elgin (MS28020LI), and as used in aircraft-carrier-based Grumman Cougar F9F-5 and North American Fury FJ2 Jet Fighters. See photo of the cockpit of the F9F-5 from its flight manual dated 1955, showing the location of the clock.
The clock winds and keeps time a few minutes. Has not been examined for accuracy or full functionality. The dial is 1 7/8 inches diameter and is ~1.5 inch deep.