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In the mid 1930’s, prior to the outbreak of war, aircraft had simple navigation aids to help find a particular airfield, however if the weather was bad with poor visibility the aircraft could not land and had to be diverted. It was recognised that this would be a severe limitation on RAF operations. The equipment chosen to overcome these limitations was mainly based on the German Lorenz beam approach, renamed Standard Beam Approach (SBA). It was widely deployed by Bomber Command throughout the war but even after much expenditure of money and effort, technical and operational problems dogged the system, but there appeared no alternative.
They were not aware that Coastal Command already had a system in operation which had been suggested by a TRE engineer attached to a station in Northern Ireland and became the first radar Beam Approach Beacon System (BABS). This relied on transmissions from the aircraft’s radar to interrogate a ground system which then transmitted wide and narrow pulse signals back to the aircraft in such a way as to enable the pilot to know whether he needed to move left or right to follow the narrow glide path required to find the runway and land visually. This was improved on by TRE at Worth Matravers to become BABS Mk1 for Coastal Command.
However with all aircraft now being fitted with short wavelength centimetric magnetron radars such as H2S, ASV Mk III and centimetric AI, a new design of interrogator was needed. Trials with a prototype showed poor performance with BABS Mk I. The need for a new mobile ground system was therefore required. The Army had been using the Rebecca/Eureka system to drop and retrieve secret agents from France, so TRE considered using Rebecca as an interrogator. Early in 1943, TRE began work on a prototype loosely based on Eureka for the ground component and Rebecca in the aircraft (BABS Mk II ??). Meanwhile Bomber Command, after another review of SBA in November 1943 it was considered inadequate. Bomber Command then stated a firm requirement for BABS Mk II to be installed in all operational and training airfields.
With the end of the war in Europe, the urgent need for the system in the UK reduced. However the system would still be required for staging posts to the Far East and the needs of the RAF’s Tiger Force allocated to the defeat of Japan. Not all Tiger Force’s Lancaster’s would be fitted with H2S, so an independent interrogator and display system was needed. TRE had already designed and tested this in the shape of Rebecca Mk IV, which could also be used in single seater aircraft so they too could safely land in bad weather.
The United States Army Air Force (USAAF) had their own blind landing system designated SCS 51, also known as the civilian Instrument Landing System (ILS) and were very anxious to test it out in operational conditions in the UK, as when they first arrived they had been taken aback by the poor weather conditions. It was decided to carry out joint RAF and USAAF trials at Defford in February and March 1944. It was fitted in a variety of US and British aircraft and proved successful and easy to learn. The USAAF adopted it at 21 airfields in the UK.
TRE, TFU(Telecommunications Flying Unit) Defford and the Americans had a common goal — how to land an aircraft without the input of the pilot. The head of the US trials team, Lieutenant Colonel Francis Mosley had a home built unit to link to the aircraft control. The Wing Commander in charge of the Defford trials, Frank Griffiths, authorised a test in a Liberator. This worked well and provided an accurate approach.
The Americans moved from Defford but TRE started a programme to develop a fully automatic landing system. The aircraft TFU choose to modify was Boeing 247-D partly because it had a very flat approach angle when landing. Further work on the aircraft and electronics enabled the aircraft to operate with the BABS system. The combination of these British and American systems led to the Boeing (above) at Defford, piloted by Griffiths, making the world’s first automatic approach and landing of an aircraft on 16th January 1945. Patents were taken out in the UK and US and the technology transferred the Blind Landing Experimental Unit at RAF Woodbridge. It would lead to the ability of today’s aircraft to land safely in all weathers.
More detail and many photos in “Boffins come to Malvern” Martin Hutchinson available at Malvern Tourist Office, MRATHS Technology Station at Malvern Railway station and Malvern Museum.
The full story is available in “Top Secret Boeing” by Bob Shaw.
M G Hutchinson