Colossus – the Computer That Helped Eisenhower’s D-Day Decision

Recently, I ran into an interesting story of how Colossus, “the world’s first electronic programmable computer,” helped Eisenhower in his British headquarters, decide to go forward with the D-Day invasion in 1944.

The text below is based on an article from The Australian…

Last week’s 70-year re-enactment of the June 6 D-Day landings in Normandy by Allied forces ­brought forth memories of one of the most important days in modern history – one that led just over a year later to the collapse of Nazi Germany, the end of the war and the death of Hitler. For some observers, it also triggered memories of the birth of modern information technology.

On June 5, 1944, a day before the invasion, commander in chief Dwight Eisenhower sat in his British HQ, mulling over whether to let the invasion go ahead across the English Channel in what was shaping as extremely stormy weather.

He was sitting on two vital pieces of information: one, predictions by British meteorologists that there just might be a short break in the weather on June 6; and two, that his opposite number, Germany’s commander in chief on the Western Front, Field Marshal Erwin Rommel, had decided the weather was so bad that an invasion was unlikely and he had left Normandy for a few days back home in Germany with his family – leaving his troops without a commander.

How did Eisenhower know this vital information? A computer told him. A computer? In 1944? That’s right – the world’s first electronic programmable computer, a mighty giant dubbed Colossus using state-of-the-art vacuum tubes, had only recently been switched on at the famed top-secret code-breaking Bletchley Park establishment in Buckinghamshire.

It had been designed by a British Post Office worker, Tommy Flowers, with help from the famed Alan Turing, to decode ciphered messages sent between the German High Command and commanders in the field, including Rommel.

And Rommel’s fateful request to leave the field would have been known in Eisenhower’s HQ within hours, if not minutes.

And so, not long after, Ike offered three of the most famous words of World War II: “OK, we’ll go.” D-Day went ahead, and Germany’s fate was sealed.

Colossus, alas, was destroyed after the war, along with Flower’s blueprints, but many of its principles were used in the first commercial – and equally massive – mainframe computers that sprang up in the 1950s and 60s.

A fully working replica of Colossus was built in 2007, and it’s on show ­at the National Museum of Computing, in Bletchley Park.