Compass Module for RAF Course Setting Bomb Sight
This direct-reading magnetic compass module was used in the "Wimperis" Course-Setting Bomb Sight of the British Royal Air Force. The compass body itself is housed within a metal container with gear teeth surrounding the base. These teeth engaged the CSBS mechanism to assist in the approach to the intended bomb target.
See an example of the bomb sight here.
The fluid from this compass has since evaporated. But it is still a fine specimen given its age. Measures approximately 4 inches diameter and 2 inches high.