Oxygen Regulator Type A-9A S2 Tracker operates in the same manner

operates in the same manner but has greater air volume capacity for larger aircraft with more air-driven instruments such as a heavy bomber or transport

with a serial number prefix of AC-39

so it could use repair

The manual is 950 pages and ~2inches thick

Oxygen Regulator Type A-9A S2 Tracker operates in the same mannerThis is a WWII era aircraft Oxygen Regulator Type A 9A as used across bomber and transport aircraft of the US Army Air Force and US Navy, such as the B 17 Flying Fortress (see image illustrating the location of the co pilot's regulator from the B 17F flight manual dated 1943). This example has a serial number prefix of AC41, evidence of a year of manufacture of 1941. The A 9A regulator was a low pressure continuous flow regulator (vs the on demand,