The aim was to send an invading force across the Channel to break through the heavy defences of the Northern coastline. Every advantage was needed, especially surprise.
MI5 was running a network of double agents whom the Germans thought were working for them in Britain but who, in reality, were controlled by the British and used to feed false information to the enemy.
Critically, ahead of D-Day, messages from MI5's double agents were coordinated to give the impression that a large invasion was imminent across the narrowest part of the Channel, at the Pas de Calais, rather than in Normandy.
And this is where East Sheen comes in.
A house in Richmond Park Road (above, courtesy of Google Streetview) was occupied by a Pole, Roman Czerniawski and his wife. Czerniawski, AKA Agent Brutus, was the survivor of a string of hair-raising adventures since the start of the war. He'd set up a network of French resistance spies, been discovered and captured by the Germans in France, and persuaded them that he would now spy for them.
He managed to get himself sent to England, where he immediately started working with MI5 to fool his German spymasters.
From one of East Sheen's innocent-looking semis, Brutus operated his radio transmitter (although the Germans were told it was his wireless operator, Chopin, who was sending the messages. Chopin didn't exist).
In hundreds of messages over a long period, Brutus had built up an elaborate story, of being part of a fictitious invading force assembling in the South East commanded by (the real) General Patton, who was seen around, to add credibility to agents' reports.
As Ben Macintyre recounts of Czerniawski's work from East Sheen, in his gripping Double Cross (2012):
"In three long reports, packed with details supposedly gathered from within the army's operations room at Staines, and tours of Kent and East Anglia, he was able to present the Germans with …'the entire chain of command of the shadow army group in southeast England.' Patton's army, he warned, gave 'the impression of being ready to take part in active operations in the near future'."
Gratifyingly, M15 later got their hands on a German map showing what they believed to be the deployment of allied forces around the UK. It corresponded almost exactly to the fictitious scenario presented to them by the double cross agents.
The result was that when the invading force landed in Normandy, at first the Germans believed it was only a sideshow, perhaps intended to fool them into lowering their defences along the coast.
Although there were 10,000 allied casualties on the first day of the Normandy landings, with 2500 killed, more than 175,000 troops were landed in France and ready to fight.
If the messages from Richmond Park Road had not been heard or believed, those casualty numbers could have been far, far worse, and D-Day might even have been no more successful than the failed Dieppe landings two years earlier.
