On 1 September 1939 Mickey Mouse put BBC Television to bed for the duration of World War II. The backroom boys hung up their white coats in Studios A & B at Alexandra Palace and mothballed the spanking new equipment including the iconic transmitter mast that dominated the North London skyline. Not quite! Some bright spark in the Ministry of Defence had an idea that the transmitter might be useful to the war effort. At the beginning of the war, exactly what use that might be was still unclear?
The story of re-commissioning the transmitter to prosecute the war was a huge state secret. Many of the BBC engineers involved signed the Official Secrets Act and until late in their lives were mostly reluctant to make their story public. There are surprisingly few public records to help historians like Dr Jim Lewis piece together the story.
The scientific boffins within the intelligence agencies tasked Professor R.V. Jones with finding out how the transmitter might be used. Based at Bletchley Park , Jones scoured pre-war files of the Secret Intelligence Services to see if their was any evidence of a German secret weapon.
At the same time as this research was ongoing in early 1940, BBC engineer Tony Bridgewater was asked to return to Ally Pally to get the transmitter up and running on a care and maintenance basis; he was almost certainly unaware of what for. They would soon be pressed into service.
By the end of 1940 intelligence reports showed that a new system was being developed because the British had clearly learned to jam that system. The Y-Gerat system was a groundbreaking a way of keeping ahead of British jamming capabilities.
By a stroke of good fortune, the Y-Gerat system was working within the same frequency spectrum (40-50MHz) as the sound and vision television transmitter at.You guessed it, Ally Pally!
In October 1940 Wilfred Pafford, another engineer with the BBC since 1932, returned to head up operations at Ally Pally for Operation Domino. He was to remain as the engineer in charge until the end of the War.
The MoD decided to set up a listening station at Swains Lane in Highgate. In a set of huts attached to a huge relay transmitter (a huge mast is still in place) used for Outside Broadcasts before the war, a domestic EMI television was modified to listen to the radio traffic between the German command station in Kassel (and elsewhere in France) and the German navigators on bombing raids over Britain.
Incoming German bomber pilots would maintain the aircraft's correct bearing by following an instrument which monitored the path of a radio beam. When the German ground station had calculated the pilot was correctly positioned over the target a message from the ground station was sent instructing the bomb aimer to release his load.
From February 4th 1941 the date of the first bombing raid using the Y-Gerat system on Britain, by pure coincidence everything was in place to give the Swains Lane and Ally Pally teams a crucial opportunity to interfere with the information being sent to the bomb aimer.
In effect, BBC Engineers had devised a system which could 'capture' the German frequency momentarily and create a 'howl round' effect in the German navigational device when the transmitter at Ally Pally was switched on. Imagine the sound when a microphone is turned up too high at a concert: All that in the flying crew's headphones.
Once the operators at Swains Lane had decided that the German navigator had missed his opportunity to identify the target, the Ally Pally transmitter would be turned to standby ready to be re-activated for the next bomb aimer.
The jamming system may have been relatively crude but it's claimed that no more than 25% of bombers on Y-Gerat controlled air raids released their bomb loads.
It's estimated that this system of jamming went undetected until May 1941. So adept had the BBC engineers become that even when the Germans suspected their system was fallible it was simply a matter of retuning the transmitter when the German operators changed the frequency. Ally Pally's role remained undetected.
The BBC transmitter can claim credit for undermining a crucial part of the technology which aimed to lay waste to many of our cities.
Wilfred Pafford has just celebrated his 101st birthday and now lives in a nursing home in Southern England, the last of the Battle of the Beam engineers.
This film footage is from the Archive Collection held by the Alexandra Palace Television Society.
~ APTS ~
Preserving the televisual past for the digital future