Difficulties of
navigation at night

The Pathfinders


Electronic warfare






Navigational technological advances

From 1942 onwards, Bomber Command’s effectiveness was transformed by new heavy bombers including the legendary Lancaster, a new commander – Sir Arthur ‘Bomber’ Harris - and new navigation equipment with code-names such as GEE and OBOE.




The first major development in navigational technology was ‘GEE’, a system perfected in early 1942. An on-board set received synchronised radio signals transmitted from ground stations in different locations in England. Two signals gave the navigator a ‘fix’ so he could work out his aircraft’s position on the route to the target at any time.

When flying near the ground stations over home territory, GEE’s accuracy was good; At increasing distances, particularly into Germany, accuracy was reduced. However, with a range of about 300 miles, GEE at least ensured that each bomber crew entered enemy territory with reasonable confidence as to their position. After a time, the Germans worked out a way to jam the system (i.e. interrupt the radio signals from England). British scientists were forced to develop new GEE systems, new frequencies and jamming of their own. (See Electronic Warfare)


  GEE navigational system


Ready for operations in December 1942, ‘OBOE’ proved to be a particularly accurate device, at least for the shorter range targets. Two OBOE ground stations in England sent out radio signals which the bomber carrying the OBOE equipment received and re-transmitted back. The stations monitored the aircraft’s progress: One station guided the aircraft along a predetermined track, the pilot receiving signals when he deviated to port or starboard; the second station measured the aircraft’s ground speed and calculated the correct moment of bomb release. Range was limited to 300 miles and since only one aircraft could be controlled at a time, OBOE was used primarily by Pathfinder Force (PFF) aircraft to drop coloured flares to visually mark the target for the main force of bombers following behind. (see ‘Pathfinders’).

After D-day in June 1944, the advance of the Allies into the continent meant the RAF could move mobile ground stations into France to extend the range of OBOE deep into Nazi Germany.


OBOE control room


‘H2S’ became available in January 1943 and was regarded at the time as astonishingly advanced. Kept top-secret for as long as possible, large bulges began appearing under the bellies of some heavy bombers. Inside was a rotating parabolic dish which mapped the ground beneath, even through cloud, onto a screen in the aircraft. The fairly blurred picture on the screen differentiated between dark areas for sea, bright areas for land and very bright for built up areas. It worked best on coastal targets or those with a broad river or lake nearby. At first, the new H2S sets were installed only in Pathfinder aircraft who flew ahead of other bombers to accurately mark the target with coloured flares. (See ‘Pathfinders’)

The disadvantage of both H2S and OBOE was that, since the sets transmitted a signal, the Germans could identify the aircraft as an enemy. Also, as was feared, it was not long before an aircraft carrying one of the top-secret sets crashed (in Holland) and the Germans could examine the H2S equipment. Within months German fighters had an airborne device for homing in on RAF bombers using H2S. Nevertheless, H2S had a spectacular effect on bombing accuracy.


  Halifax bomber equipped with H2SH2S radar

H2S control roomH2S set


British scientists kept working to give the RAF a technological advantage and produced the even more advanced ‘GH’ in 1944. GH equipment onboard RAF bombers sent radio pulses to two ground stations in Britain, which re-transmitted them back to the aircraft. By measuring the time interval between the outgoing and returning pulses on an oscilloscope display the navigator could direct the pilot towards the target and determine the precise point for accurate bomb-release. This system only could be used by a limited number of aircraft at any one time and had the same range as OBOE (around 300 miles) but it improved the RAF’s bombing accuracy even further.


Hi-tech raiders

From the first tentative raids during 1939-41 using sextants and ‘dead reckoning’, Bomber Command had gradually evolved, with the help of complex navigation aids and radio counter measures, (See Electronic Warfare) into a high-tech striking force of devastating power and effectiveness.


  Airborne radar