The importance of maps to the military can scarcely be underestimated. Whether it is to navigate to an enemy position, design a bridge or bring down artillery fire; maps are used every day by the armed forces. To accurately plot a position on a map or to draw a map from scratch, the ability to transfer bearings onto the page is essential and for this a protractor designed to be used with military maps is very helpful. This example, although not /|\ marked, is one issued to British Army Officers:This example is marked ‘Protractor Rectangular ‘A’ Mk III’ (6”x2” Exactly). This mark of protractor seems to date from the 1920s- the Mk IV was introduced in about 1930. It is made of celluloid by Reeves & Sons Ltd of London and in addition to the angles around the edge has multiple lines for different scales of maps on both sides:The 1929 copy of ‘Notes on Map Reading’ explains about the scales:
The Service Protractor Mark IV shows scales of ¼ inch and 1 inch to the mile; also scales for R/Fs of 1/25,000, 1/50,000 and 1/250,000. Thus the normal scales of British maps can be drawn from the protractor.
The protractor is designed to fit snuggly into a pocket on the underside of the lid of the map case (here):These protractors were also made of ivory, brass and wood, for more details of the many different types of military protractor please look at this excellent webpage here.