Hill's main contribution was in working with gunsights and armament trials in which he could bring to bear his mathematical abilities. In accordance with civil service practice at the time discoveries made by civil servants could be patented by them. He was awarded several secret patentsUK patent numbers 404362, 336030, 404719, 452915, 396108 and 1923 patents 20308 and 31614 and 1935 patent 15885 relating to reflector gunsight improvements, including the ability to adjust for range. He also patented the use of monochromatic light in gun sights (the 1920s equivalent of the modern red dot sight) and was awarded patents for improvements to machine gun muzzle locks and machine gun synchronisation gear. The reflector gun sight patents were later assigned to Barr and Stroud and used in the guns sights they supplied to the RAF during World War II including the GM2 reflector fixed sights used in fighters from 1938 and the Mk III reflector free sights used in bombers and adopted by the US Navy as the Mark 9.
