Finding and maintaining the correct course to target was a vital but difficult job for early pilots, who used compasses and maps to establish the plane's bearing (direction) and position; and calculated speed with the classic technique of 'dead reckoning'– spotting two landmarks and noting how long it took to get from one to another.

This was the state of the art when Bomber Crew began flying. It's no surprise that the accuracy of early bombing raids was low, and a 1941 report concluded that two-thirds of planes were never closer than five miles to their target. Things began to change with the introduction of 'Gee' in 1941, a system in which an interlocking grid of beams, projected from three radio stations, was displayed on an on-board receiver from which a navigator could establish the aeroplane's position to within a few kilometres.

After 'Gee' came 'Oboe': two radio beams tracking a single aeroplane, to keep it on course and indicate when it reached the target. Accurate to around 100m, 'Oboe' had a shorter range than 'Gee' and was typically used to guide Pathfinder aircraft, which flew ahead of bombers and dropped flares over the target.

The new technology of radar, initially deployed in British night fighters, also played a part in navigation. 'H2S', an air-to-ground radar system, was introduced in 1942, and below a certain altitude enabled crew to 'see' the target area, even at night and through cloud cover. Pathfinder aircraft in particular achieved a high degree of accuracy with 'H2S' and 'Oboe'. Unfortunately, 'H2S' equipment emitted signals which could be detected and jammed by German aircraft, and by the end of the war jamming and counter-jamming was a thriving industry.

The rapid advances made under the pressure of war led to further development of long-range radar- and radio-based navigation aids. Between 1978 and 1989 the US Department of Defense set up the Global Positioning System (GPS): a network of 24 satellites carrying atomic clocks, whose signals can establish a position anywhere on earth to within 20 metres. Military aircraft now use GPS receivers; cheaper devices are fitted in cars or embedded in watches.

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The crew work on their navigation skills