Compass, Magnetic Direct Reading, Type B-16 US Army Air Force WWII
The Army Type B-16 Direct Reading Magnetic Compass was used across a number of US Army Air Corps and Air Force aicraft during WWII, including heavy bombers B-17, B-24, B-29, medium bombers B-25 and B-26, as well as light bomber A-20, according to the Accessories Interchangeability Chart dated Feb 1945. It was also used in versions of US Army Air Force WWII fighters P-38, P-39, P-40, and P-47, as well as transports C-46 and C-47. This model was made by Bendix/Pioneer Div, part number 1818-1-A.
According to the spec sheet in the Index of Army Aeronautical Equipment -Volume 6 Instruments:
Pilot's compasses are direct reading magnetic type compasses. They consist of a fluid filled bowl which contains a pivoted float bearing magnetized needles. The float is suspended so that the needles are free to align themselves horizontally with the earth's magnetic field. One end of a magnetic needle, called the North-seeking end, always points toward magnetic North when freely suspended.
In such compasses, the position of a graduated card attached to the float is visible through a glass cover in the front of the bowl. The bowl is filled with compass fluid to dampen the movement of the card, which is marked with the cardinal headings (North, East, South and West).
In steady flight, the needles point continuously toward magnetic North. A box, containing magnets which compensate for deviation, is located on top of the compass. The lubber's line, a piece of thin metal placed vertically in the center of the glass cover or window, intersects the card, to show the direction in which the airplane is pointing.
This example shows its age, but remains in decent condition. It is mostly filled with fluid and the compass card rotates. Measures 3.25 inches diameter and ~4.5 inches deep.