It is liquid filled and mainly made of brass, there is a lighter version, the M88 that is alloy but I do not begrudge the reassuring weight in my pocket.
While not completely “squaddie proof” it is well made and robust enough to not worry too much about in
normal use. As with any precision instrument, a little respect in handling is wise.
You can see the mother of pearl compass dial, with it’s finely graduated scales, through the window in the lid but when opened up, a second dial is revealed with a coarser scale, marked in 5° increments. This is for setting a bearing to march and it is locked by a knurled knob at 45° from the Lubber line.