Stalling Speed Signal Assembly, Type D-3, WWII US Army Air Force, 1942
Here is a fine example of a WWII-era Stalling Speed Signal Assembly, US Army Air Force Type D-3, made by US Gauge, part number AW-SS-1-C. It has a serial number prefix of AF 42, indicative of a 1942 manufacturing date. It comes with an original Handbook of Instructions and Parts Catalog dated May 15, 1942 (12 pages printed front/back).
The module was used in training versions of pursuit aircraft with instrument flying hoods installed, such as the P-40. Pitot-statically-driven as evidenced by its rear ports marked S (static pressure) and P (pitot pressure), the unit would automatically release the instrument flying hood when the aircraft approaches airspeed limits, lower or upper from 100-400 MPH, which could lead to a stall, as set by the pilot, or by the ground crew pre-flight.