Pilot Localizer / Glide Path Indicator I-101C for A-1 Runway Localizer System
This is a WWII-era Pilot's Localizer/Glide Path Indicator used in the Modified A-1 Runway Localizer System of the Instrument Approach System of the US Army Air Force and US Navy. Used in conjunction with the Radio Bearing Indicator (i.e., Radio Compass), the indicator guided the pilot to the correct course and glide path for a proper landing in conditions of poor visibility. The system was used across many bomber and transport aircraft of the US Army Air Force and the US Navy.
If the aircraft was approaching along centerline of the runway, the vertical needle would appear centered on the indicator's vertical centerline as shown in the photograph. If the aircraft was right of the runway, the vertical needle would appear to the left of the centerline, and vice versa.
If the aircraft was approaching the runway on the correct glide path, the horizontal needle would align with the indicator's horizontal centerline as shown in the photograph. If the aircraft was angled above the correct glide path (in which case the aircraft would overshoot the runway), the right end of the horizontal needle would angle downward, directing the pilot to increase the angle of descent. If the aircraft was angled below the correct glide path (which would cause the aircraft to land short of the runway), the right end of the horizontal needle would angle upwards, directing the pilot to decrease the angle of descent. See images in photo gallery from the Instrument Approach System Manual dated 1943 (the full manual can be downloaded by clicking here).
This instrument was eventually removed from an aircraft of the US Navy on or about 1954 as evidenced by its yellow date stamp from Naval Air Station (NAS) Alameda (CA). These instruments were developed in conjunction with the US Army Signal Corps, hence it's stamp on the rear case. It is in relatively good condition given its age. The glass, case, and needles are intact. There is evidence of slight moisture ingress just under the glass (white glaze), but otherwise it is in very good condition. Measures 3.25 inches diameter and ~3 inches deep.