Turn and Bank, Pre-WWII, Model 1923, Air Service US Army
Here is a rare, early 1920's-era Turn and Bank Indicator, Pioneer Model 1923, made for aircraft of the Air Service US Army, which was a post-WWI precursor (from 1918-1926) of today's US Air Force. The serial number prefix is "25", which we believe indicates a manufacturing year of 1925.
See the description of this indicator in the excerpt from Aviation Week January 29, 1923, when it was introduced.
Besides its early design, what makes this Turn and Bank Indicator quite unique is its On/Off knob, which controls air flow to the externally-mounted venturi tube and the indicator's internal gyro.
The glass lens is intact, as is the glass banking tube, ball, and its fluid. The On/Off knob turns as well. Measures 2.75 inches diameter and ~5 inches deep. A superb example of a rare instrument.