At a crucial stage of World War II, the Special Operations Executive deliberately allowed one of its most closely guarded top secrets to fall into Nazi hands – as part of a grand deception plan.
In 1944 SOE planners wanted to make the Nazi high command think that there was an extensive underground resistance developing within Germany itself, to make the SS and Wermacht waste weapons and men chasing a will o the wisp. The operation – codenamed Periwig – involved simulating the existence of a German resistance similar to the French resistance.
To convince the German secret service , the Abwehr, of Periwig’s authenticity, SOE dropped canisters of arms and fake instructions from London at remote spots in Germany and on the Polish borders, knowing some of them would be found and investigated at high level. They also produced a lot of fake radio traffic aimed at supposed German underground patriots, which the Abwehr’s listening service would be bound to detect.
But there was a problem. As London had no real network of agents in Germany, there was no return radio traffic back to London – an absence that was bound to give the game away.
SOE’s technical department had been developing secret radio equipment throughout the war, especially the iconic B2 suitcase radio, dropped in hundreds to agents in France and elsewhere. By 1944, the SOE engineers had developed a top secret technology that would later form the basis of most espionage communications – the burst transmitter.
In its simplest form, a message would be encoded and recorded – on punched tape or magnetic tape. This recorded version would be run through the clandestine radio transmitter at very high speed so that the message was sent in a single burst lasting only seconds, rather than minutes – giving the enemy listening stations no time to locate its position.
But thought SOE had developed the burst transmitter, it proved difficult if not impossible to use in practice. With the technology of the day it was simply too difficult to detect, record and decode burst messages.
The Periwig planners persuaded the high command to allow some burst transmitters to fall into the hands of the Abwehr, knowing that their engineers would realise their significance. This not only explained the apparent absence of return traffic to London, it also induced the Nazis to waste even more resources attempting to combat a threat that did not exist.
At this distance of time, one can only marvel at the nerve it must have taken to disclose the secret to the enemy in the hope that it would plant a seed of deception.