The M2 Artillery Compass is a special-purpose instrument designed for high accuracy. It combines a surveyors compass with a clinometer, level and a plumb built into one instrument. It was in use during World War II, based on an earlier Compass, M1 that was not graduated in mils. The M2 has readings for 0-359 degrees or 0-6400 mils.
The M2 Compass is the military version of the Brunton Pocket Transit. It was issued originally with a good quality leather case but more recently comes with a plastic case.