James Stagg

Born on 30 June 1900 in Dalkeith, Scotland, James Stagg was a British meteorologist who persuaded US General Dwight Eisenhower to change the date of the D-Day invasion based on the weather. Stagg attended the University of Edinburgh and then became an assistant in Britain’s Meteorological Office in 1924. In 1932–33, he led the British Polar Year Expedition to the Canadian Arctic, and in 1939 was appointed superintendent of the Kew Gardens observatory, home of the Meteorological Office. In 1943 Stagg joined the Royal Air Force Volunteer Reserve and served as the chief meteorological officer for Operation Overlord—the code name for the Allied invasion of German-occupied Western Europe.

The assault over the English Channel had been tentatively planned for the early hours of 5 June 1944, when there would be a full moon and the tides would be low enough to expose underwater obstacles placed by the Germans. However, the weather posed a problem because of impending storms. It was Stagg who made the call and advised Eisenhower to delay the invasion by one day, to 6 June, when he believed there would be a temporary break in the weather. The decision has been called the most important weather forecast in history: Not only did the invasion take the Germans by surprise, but a major storm during the next available period, 18–20 June, would have delayed the invasion even further. (The dates for a potential invasion were driven largely by tides—see Physics Today, September 2011, page 35 .) Stagg was knighted in 1954 and continued to serve at the Meteorological Office until 1960. He died in June 1975. Stagg has been portrayed several times in movie and television depictions of D-Day, notably by Patrick Barr in the 1962 film The Longest Day, by Don Gallagher in the 2004 TV miniseries Ten Days to D-Day, and by David Haig in his own 2014 play Pressure.

Date in History: 30 June 1900