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The dial needed to be light silver or white (like enamel). The case could be made from steel, chrome or hardened brass. The hands should be made of blued steel and the case should have a rotating lunette. The movement should run for a minimum of 36 hours (fully wound). The movement needed to be wound by the crown instead of using a separate key. VIIA needed to meet the following requirements of Building Specification G.535 : The British Weems 6B/159 with specification Mk. The bezel lock is at 2 o’clock, and the bezel has a noticeable slope. However, the 27mm diameter type A-11 was standardised by the United States Army Air Forces in May 1940, and had leaf hands as did the commercially available second setting watches at the time.

The American Weems A-11 was initially manufactured in accordance with US military specification 27834, published in August 1937, and the British 6B/159 met specification G.535.ĭuring the meetings, the Air Ministry deemed the A-11 Weems model too small at 27mm diameter, but Longines had produced a larger 34mm version since 1937 which the Air Ministry liked. The watch was to have a hacking facility, and the Weems second setting rotating bezel had provided this in a robust way, helping to simplify avigation for about 10 years.

This needed to be simple to use for dead reckoning navigation.īritish and American air forces held joint meetings regarding the design of the American A-11 watch, which in Britain was to be sourced for the RAF and labelled the 6B/159. One item which needed to be procured was a hacking watch for navigators to assist with accurate navigation. The RAF expansion schemes from 1934 to 1939 provided the opportunity for forward planning for the RAF and this was accelerated after the declaration of war in 1939.