US3940.)WWII US MILITARY AVIATION INSTRUMENT, PILOT DIRECTION INDICATOR: heavy bomber instrument as detailed in the description below found on the internet. This instrument allowed the navigator to send direction data to the pilot on the bomb run approach. Heavy, smooth black finished body, glass face and completely intact. Attractively mounted to clear lucite stand. With luminescent dial having needle indicator and 'PDI' (Pilot Direction Indicator). Even has the original screws that mounted it to the instrument panel. Has aviation instrument maker 'Made by ROLLER-SMITH CO, Bethlehem, PA'. Note the on-line narrative below which details the use of this PDI instrument, it's model type and the aircraft that employed it. EXC++++

The Pilot Director Indicator (PDI) was used during WWII in bombers of the US Army Air Force, including heavy bombers B-17 Flying Fortress, B-24 Liberator, and B-29 Superfortress and medium bombers B-25 Mitchell and B-26 Marauder, and US Navy's PBY5A Catalina and PB4Y Privateer.  

The PDI was located on the pilots instrument panel, and received signals from the bombardier to indicate his desired course changes, left or right, to obtain an accurate bomb run.  It was used in aircraft with the C-1 Autopilot system, or in those without the C-1, it received its signals from a Type A-1 pilot indicator director control. See the spec sheet from 1944.