This is a lensatic compass, a type of compass often used for military and survival navigation.
It is designed for precision, allowing users to sight a target and simultaneously read the bearing.
The compass has a sighting wire in the cover and a sighting lens to help align with a distant object.
The dial has two sets of numbers: one for degrees (0 to 360) and one for mils, which are used for more precise measurements.
The liquid-filled capsule helps to dampen the needle's movement, providing a more stable and accurate reading.
See photos closely for actual used condition and measurements.