How much did the Soviet Union know about D-Day before it happened?
Although the timing of D-Day was the most closely guarded secret of the war, Churchill had in fact told Stalin many of the details months beforehand.
The Soviets had been impatient for the opening of a second front in Europe ever since the Germans invaded the Soviet Union in June 1941. But Stalin was suspicious – on account of Churchill’s well-known antipathy to communism – that the Allies planned to withhold aid from their Soviet allies. However, Churchill was strategically wise and realised that the USSR needed help, for its collapse would allow the Germans precious time and resources.
Assaulting the Germans from Normandy was ultimately the best way of helping the Soviets. Churchill continuously promised Stalin an invasion but, before he could deliver, he first needed the Americans to join the war on Germany. He also realised that the US army needed combat experience of fighting the Wehrmacht, something the Americans themselves did not immediately grasp. As such, at the Casablanca conference in January 1943, he resisted early plans for a cross-Channel attack.
This delay frustrated the Americans and annoyed Stalin, both assuming that Churchill was running shy of a contested beach landing. But it was impossible for the British leader to resist combined Russo-American pressure at the Tehran conference in November 1943. This resulted in an agreed invasion of France in spring/summer 1944 – known as Operation Overlord. The chosen area of Normandy was confirmed in January, with Churchill boasting to Stalin of the construction of two artificial harbours.
Thus, the Soviets (unlike the French Resistance) were aware of many of the details far in advance. On the day, Soviet and Chinese observers watched the landings from HMS Warspite. Two weeks later, Stalin launched Operation Bagration, to directly complement Operation Overlord – proof, if any were needed, that the Allies could operate in concert against the Third Reich. Peter Caddick-Adams, author of Sand & Steel: A New History of D-Day (Arrow)