Storm over the Channel 4–5 June 1944

You are advising General Dwight D. Eisenhower, Supreme Commander of the Allied Expeditionary Force.

The Allied invasion of Normandy has already been postponed by 24 hours because of stormy weather. Tens of thousands of troops are waiting in ports and aboard ships. Group Captain James Stagg, the chief meteorologist, reports that a short break in the weather may arrive.

Known information

The landings need a particular combination of tide and moonlight that occurs only on a few days each month.
If the next few days are missed, the next suitable tides are about two weeks away.
Stagg forecasts a temporary improvement for 6 June, but conditions will still be marginal and the forecast is uncertain.
Rough seas and low cloud would make landing craft, airborne drops and air support less effective.
Keeping the invasion secret for another two weeks, with troops already briefed, would be difficult.

Reveal what happened (spoilers: decide first)

Fact

What actually happened

Eisenhower ordered the invasion to go ahead on 6 June 1944. (Go on 6 June)

Based on Stagg’s forecast of a temporary break, Eisenhower ordered the invasion to proceed, and the Normandy landings took place on 6 June 1944. More than 150,000 Allied troops landed that day. When the next suitable tides came in mid-June, the Channel was hit by what Stagg later called the worst Channel weather for 20 years.

Important

Possible consequences · Analysis and speculation, not fact

Historians generally think a two-week delay would have raised the risk of the plan being discovered and, given the mid-June storm, might have pushed the invasion back further still. How Germany would have used that time is a matter of analysis rather than fact.

History does not reveal what would definitely have happened under the other choice. Many factors could have changed the outcome.

Context · Why it was decided this way

The forecast drew on several meteorological teams who did not fully agree. The Allies had access to weather observations from across the Atlantic that German forecasters lacked, and German meteorologists did not expect a landing in such unsettled conditions.

Eisenhower also wrote a short note, to be used if the landings failed, taking personal responsibility for the decision. After the war Stagg reported the conditions the fleet would have met in mid-June, and Eisenhower replied thanking “the Gods of war we went when we did.”