Bletchley Park and D-Day

Kept secret for decades, Bletchley Park’s codebreaking played a vital part in D-Day, saving thousands of British and American lives.

By Bletchley Park

Bletchley Park, UK

Enigma message transmitted at 01:52 hours by the German navy on D-Day (1944-06-06) by Bletchley ParkBletchley Park

As dawn broke on D-Day, 6 June 1944, Allied troops waited off the coast of Normandy. The largest amphibious invasion in history was about to begin.

A rare collection of Enigma messages sent on D-Day by the German navy, and broken at Bletchley Park, gives a blow-by-blow account of the action.

As events unfold, confusion gives way to a realisation of the scale and importance of the invasion.

Intelligence from Bletchley Park played a crucial part in the operation’s planning and execution.

The picture of German defences pieced together by the Codebreakers would shape the events of D-Day.

Sent at 01:52 hours (European summer time) on D-Day, this is the first message in Bletchley Park’s collection.

Its order of ‘Immediate readiness’ to all units of the Second Defence Division hints at German command’s first inkling of what was taking place.

We do not know what triggered this warning, but it is likely they had received reports of increased naval activity and the first parachute landings.

Bletchley Park was set up to intercept, decipher and translate messages on D-Day in as little as 2.5 hours.

TOI, at the top of the message, shows the Time of Intercept - when the message was intercepted by Allied wireless operators listening in to German transmissions.

TOO is the Time of Origin of the message, given in European summer time - two hours ahead of GMT.

At the bottom of the message is the time it was translated at Bletchley Park.

Enigma message transmitted by the German navy at 01:55 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

Not all the D-Day invasion activity was real.

The Allies dropped 500 dummy paratroopers in various locations to distract attention from the real parachute landing zones.

This message shows that the Germans didn’t fall for the ruse.

“Sea Defence Commandant NORMANDY” was Konteradmiral Walter Hennecke, who oversaw the naval defences from his headquarters in Cherbourg.

Here, he reports back to his direct superior in Rouen.

Enigma message transmitted by the German Navy at 06:03 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

Fighting at sea was intense.

At 04.55 nine German vessels left Le Havre, ordered to sweep the coastline for enemy craft.

At around 05.40 they stumbled upon the Allied fleet and, immediately receiving heavy fire, quickly launched eighteen torpedoes.

The battleship HMS Warspite achieved a direct hit on one of the German patrol boats. Here, its commander, Viktor Rall, reports the loss of the vessel.

Enigma message transmitted by the German Navy at 07:39 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

As well as sea vessels, the German navy also controlled numerous coastal gun batteries.

One of the most important batteries, with three 210mm guns, was at Saint-Marcouf, near Utah Beach. Its commander was one of the first to report sighting the invasion fleet.

The battery engaged the Allied warships and succeeded in sinking the destroyer USS Corry (here mistakenly identified as a cruiser). However, fire from other ships quickly knocked out one gun.

Enigma message transmitted by the German Navy at 08:35 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

By mid-morning, German naval commanders were beginning to realise the scale of the operation. Allied troops had landed on all five main beaches and the fleet continued its bombardment of the coastal batteries. 

Vierville and Colleville were the villages behind Omaha Beach, one of the two beaches allocated to American forces, where a bloody battle was taking place.

Just to the West, US Army Rangers had scaled the steep cliffs to reach the gun battery on the Pointe du Hoc.

The area from Ravenoville to the Vire estuary was the location of the other American beach, codenamed Utah, which had been secured against little opposition early that morning.

Enigma message transmitted by the German Navy at 09:25 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

An hour later, word had been received from the naval installation at Arromanches that tanks were ashore. This was the landing of the British 50th Infantry Division on Gold Beach.

By midday Arromanches was reported to be surrounded, and Hennecke’s evening report would state “Fate of ARROMANCHES personnel uncertain”.

Enigma message transmitted by the German Navy at 11:30 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

The German navy was even involved with fighting some distance inland.

The crossings over the river Orne and Caen Canal at Benouville, which controlled the left flank of the beachhead, were famously captured in a daring midnight glider landing; the canal bridge became known as Pegasus Bridge.

In the late morning two German craft from Ouistreham approached the bridge, apparently unaware it was in enemy hands.

One boat was hit by a shot from a PIAT anti-tank weapon and ran aground, where the crew were captured. The other retreated, sending this report on the encounter shortly afterwards.

Enigma message transmitted by the German Navy at 17:40 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

In the late afternoon Admiral Theodor Krancke, who commanded all German naval forces in France, issued this situation report from his headquarters in Paris. The main landing areas had now been identified, and he believed that the main danger lay in the British and Canadian sector. 

However, the perception that the Omaha Beach landing had been “cleaned up” was incorrect.

By this time American troops had overcome the defenders and were pushing inland.

Enigma message transmitted by the German Navy at 21:05 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

A further surprise was yet to come.

Late in the day the Allies launched a second massive airborne drop to reinforce both flanks of the beachhead. 208 gliders carrying 1,347 troops landed in the American zone, as reported here; six minutes later, a further 246 appeared, bound for the British sector.

Troops of the 21st Panzer Division were demoralised by the sight of the airborne armada. Their commanders, wary of being outflanked from the air, ordered them to fall back.

Enigma message transmitted by the German Navy at 22:52 hours on D-Day (1944-06-06) by Bletchley ParkBletchley Park

The Marcouf Battery was still holding out, although it had been forced to shell a nearby beachfront “resistance nest” (“WN”) which had been captured by the enemy, and had lost a second gun.

For his actions on D-Day, Hennecke recommended Walter Ohmsen for the Iron Cross that very evening.

D-Day: Interception, Intelligence, Invasion immersive cinematic experience at Bletchley Park (2019) by Andy Stagg, courtesy of Bletchley Park TrustBletchley Park

By the end of 6 June, about 150,000 Allied troops had landed, ready to push inland in the coming months.

Bletchley Park’s secret intelligence had played a vital part in D-Day, giving the Allies their best possible chance of success.

The Supreme Commander of the Allied Expeditionary Force, General Eisenhower, wrote that the Codebreakers had “saved thousands of British and American lives”.

Kept secret for many decades, their full contribution is now revealed in a new immersive cinematic experience at Bletchley Park: D-Day: Interception, Intelligence, Invasion

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