Main Navigational Systems Used by RAF Bomber Command and RAF Pathfinders
At the start of WW2 the RAF was dependent on non-radar aids for safety and navigation such as position fixing medium and high frequency direction finding MF and HF DF which required the use of wireless equipment and a wireless operator.
The “ Darky” system was another position fixing procedure that used R/T ( Radio ) so that the pilot could speak to a ground station when over the UK and ask for his position. He would be given his approximate position and/or courses to steer and distances from ground station to ground station until he eventually found his own airfield. Darky was intended for the use of aircraft in distress or lost over Great Britain and was eventually superseded to a large extent by Gee.
In the early days of WW2 bombers were expected to bomb by daylight and deliver accurately. Varying winds plus cloud cover, fog, mist and/or industrial haze frequently obscured targets so bomb release was made by dead reckoning from the last navigational "fix". The bombers dropped their loads according to the estimated time of arrival for the target. The RAF soon found that daylight bombing resulted in heavy losses due to frequent fighter interception and therefore switched to night bombing. This allowed the bombers a better chance of survival but was considerable harder to even find the general area of the target let alone drop bombs precisely.
However the RAF continued bombing by day at low level on a much smaller scale on special high value targets with mixed results. The specialist De Havilland Mosquito Squadrons were particularly effective in this role as WW2 progressed
From 1942 the new generation of radio and radar systems being introduced played an increasing and crucial role in Bomber Command navigation and the ability to find and hit targets.
The first mention I can find of Gee in the 103 Squadron Operational Record Book ( ORB ) is in September 1942 at the time the Squadron converted to the Handley Page Halifax when training on “G” is mentioned in the training monthly summary and continued to apply to the Avro Lancasters which replaced the Halifax at the end of October 1942. Also the 576 Squadron Lancasters will have been fitted with Gee as standard at their formation at the end of 1943.
In February 1944 the 103 Squadron ORB monthly training summary starts to log a significant number of “ Y “ or H2S cross country and “Y “ or H2S practise bombing details. “ Y “ being another term for H2S
Similarly with 576 Squadron who had a lecture on the new system in March 1944 and H2S practise details start to appear in the 576 Squadron ORB from then on.
G-H or Gee H was a much refined and improved version of the original Gee system and I have never seen any mention of this being fitted to 103 or 576 aircraft.
The Oboe blind bombing system was the other major innovation but was only used by highly specialist Mosquito Pathfinder Squadrons
….......
GEE. A radio navigation system used by the Royal Air Force during WW2. This measured the time delay between two radio signals to produce a fix, with accuracy on the order of a few hundred metres at ranges up to 350 miles or thereabouts. Gee was the first hyperbolic navigation system to be used operationally entering service with RAF Bomber Command in 1942.
Gee came into service on the 8/9 March 1942 in an attack on Essen when the leading aircraft of the 211 force were fitted with the system. The results were disappointing as Essen was at the limit of Gee range and accuracy diminished over distance but in the weeks that followed results steadily improved. The Cologne attack on the 13/14 March 1942 was much improved.
Gee enabled bombers to reach the target within a range of 350 miles and for longer distances set them well on track after which the navigators could calculate their course with confidence. The Germans however quickly discovered how to jam Gee and it soon became impossible to obtain fixes beyond the Dutch coast. Nevertheless navigators used it to maintain an accurate track over the North Sea outbound and on the final leg of their journey inbound to their base and this was its great value. One of the major advantages of Gee was that it was a passive system requiring a receiver but no transmitter. From three widely spaced ground transmitters stations situated on a baseline about 200 miles in length radiated sequential radio pulses laid down in an invisible grid. One transmitter station was known as the A or Master station while the other two were B and C or Slave stations. By measuring the distance in time taken by A and B and A and C signals to reach the aircraft
Each Slave station was locked on to a Master transmission. By measuring the time taken by the A and B signals and A and C signals to reach the aircraft the aircraft could be located on two position lines or Gee co-ordinates and its ground position coincided with the point at which these intersected. These were printed as a grid on special Gee Charts. The data was displayed on a cathode ray tube on the navigators table in the aircraft and a good navigator could obtain a fix in less than a minute with accuracy between a half a mile and 5 miles depending on his skill. Because Gee signals were depended on ground stations in England effective rage was limited by the curvature of the earth to about 350 miles which was just enough to cover the Ruhr industrial heartland of Germany. However the general rule was the greater the range the lesser the accuracy.
….......
H2S. This was the first airborne, ground scanning radar system. It was developed for Royal Air Force Bomber Command during WWII to identify targets on the ground for night and all weather bombing. This allowed attacks outside the range of the various radio navigation aids like Gee or Oboe.
It was the only one of the three wartime navigational aids which was self contained in the bomber and not limited by range and altitude. Radar transmissions from a downward looking rotating radar transmitter fitted in the belly of the aircraft scanned the terrain below and the echoes bounced back to the receiving equipment and were displayed on a cathode ray tube in the navigators compartment painting a radar impression of the ground over which the aircraft was flying. The contrast between land and water was very evident but less so over built up areas. Over large urban areas like Berlin and its suburbs it was virtually impossible to identify anything clearly on the screen.
In conditions of total darkness and complete cloud cover a blind bombing run could be made with a good deal of accuracy using H2S and the bombs dropped blind but this method was by no means as accurate as Oboe marking.
However H2S had two important drawbacks :-
1/ From January 1944 H2S transmissions by the bombers could be detected by the Germans and night fighters were fitted with a specialised search apparatus called Naxos. This was by a no means perfect but the night fighters found it useful for finding the bomber stream at ranges as great as 22 miles but could not use it to home in on individual aircraft.
2/ The Germans also developed a highly sensitive ground based detection system called Korfu which enabled them to keep a constant plot on the bomber stream from take off to landing. It was so sensitive it could even detect transmissions from bomber aircraft parked at dispersal testing the H2S equipment prior to an operation.
..........
Oboe. A British bomb aiming system developed to allow their aircraft to bomb targets accurately in any type of weather, day or night. Oboe coupled radar tracking with radio transponder technology. The guidance system used two well separated radar stations to track the aircraft. Each Oboe tracking station used radio ranging to define a circle, the radius of which was the distance from the station to the target, the third point in the triangulation. The two circles intersected at the target. Radar pulses from each station were picked up by a transponder mounted in the aircraft. The aircraft transponder transmitted the signals back to the stations, after a slight delay. By assessing the time it took for the signal to return the distance between the station and the aircraft could be determined. One tracking station, the Cat station, was used to adjust the aircraft's flight path. The other station, the Mouse, was used to key the bomb release point.
Oboe pulses travelled at a tangent to the earth's surface and for this reason range was limited only by the height that could be reached by the controlled aircraft.
Because of the higher service ceiling of the Mosquito when compared with other Bomber Command aircraft it was the aircraft of choice and used exclusively by the Pathfinder Force.
The high flying and fast Mosquito proved very difficult for the Germans intercept and they never had much success even with the Me262 jet. Towards the end of the war the Oboe was used by both Lancasters and Mosquitos as formation leaders on daylight attacks
Gee-H, sometimes written G-H or GEE-H. A radio navigation system developed by Britain during World War II to aid RAF Bomber Command. The name refers to the system's use of the earlier Gee equipment, as well as its use of the "H principle" or "twin-range principle" of location determination
Gee-H was a combination of Gee and Oboe performing much the same job as Oboe and at much the same range. Its big advantage was that it could be operated by up to 100 aircraft at a time but its drawback was that unlike Gee and H2S it could not be used simultaneously by the main force as a whole. An aircraft fitted with G-H transmitting and receiving equipment depended on transmission to and from a pair of ground stations. The ground position of the aircraft could be measured by plotting the point at which the two lines from the ground stations intersected. Although like Gee its brange was limited its accuracy did not diminish over distance. It was not until June 1944 that Bomber Command began to make extensive use of G-H for formation daylight bombing and an urgent requirement was made for all 3 Group Lancaster aircraft to be fitted with G-H
Progress was slow and by October insufficient aircraft had been so equipped. IN order to make full use of the equipment G-H crews were trained for marking duties for night raids and act as formation leaders for daylight attacks.
Similar in operation to Gee the American Loran system was a hyperbolic navigational aid designed originally for use over water and with a range of 1400 miles. The device was first used operationally by the RAF on 11/12 November 1944 against Hamburg but its use was restricted and only fitted to aircraft of 5 and 8 ( PFF ) Groups and heavy aircraft of the 100 ( BS ) Group. Loran suffered a number of shortcomings and was very susceptible to German jamming. However it did have potential for development as a long range navigational aid and may well have been used more had WW2 lasted longer.
This topic is of particular interest and I will expand this article in more detail in due course.
|
