These three were artillery fire control instruments (TM9-2300 of Feb 1944 describes) used on a surveyors-type tripod (Tripod M10). The whole thing was described as 'Instrument, Azimuth, M1918A2 or M1'. All were 'limited standard' or 'substitute standard' by WW2. To somebody who has got any of them it is no doubt desirable.