In 1926 a meeting was held in Tavistock, Devon with representatives from the Admiralty, the War Office and the Ordnance Survey and Cooke, Troughton & Simms, E. R. Watts and C. F. Casella & Co. On Dartmoor a comparison was made between the products of UK companies and their European competition, especially the Wild T2 theodolite which pioneered enclosed glass circles rather than exposed brass ones.

The unusual circle reading eyepieces which projected out from each side arose from a wish to avoid infringing the Wild patents.

[5] where the increased accuracy made it suitable for primary surveys of Canada, Australia, New Zealand, the East African Arc and the retriangulation of Great Britain.

[6][7] In response to user requests a second, lighter version the Geodetic Tavistock appeared in 1937 [8] By 1932 the depressed state of trade had reached a point where the York factory was working at only 40% capacity but was kept going making optical components for Vickers Armstrong and also building the Vickers Projection Microscope.

The firm's telescope-making business was acquired by Sir Howard Grubb, Parsons and Co. Ltd.[12][13][14] At the outbreak of war in 1939 the UK government placed large orders for military sighting telescopes and theodolites.

[15] At the end of the Second World War, a film entitled Cooke Troughton & Simms in Wartime 1939-1945 was released which documented the manufacturing processes used to produce many of the optical instruments which were used in tanks, aeroplanes and on ships.