Message #151167

[Measured Justice]

The earliest use of these terms by the U.S. Army that the Center of Military History has been able to find was during World War I. In Field Order Number 9, First Army, American Expeditionary Forces, dated 7 September 1918: "The First Army will attack at H hour on D day with the object of forcing the evacuation of the St. Mihiel Salient."

D-Day for the invasion of Normandy by the Allies was originally set for June 5, 1944, but bad weather and heavy seas caused Gen. Dwight D Eisenhower to delay until June 6 and that date has been popularly referred to ever since by the short title "D-Day". (In French, it is called Le Jour J.) Because of the connotation with the invasion of Normandy, planners of later military operations sometimes avoided the term to prevent confusion. For example, Douglas MacArthur's invasion of Leyte began on "A-Day", and the invasion of Okinawa began on "L-Day". The Allies proposed invasions of Japan that would have begun on "X-Day" (Kyūshū, scheduled for November 1945) and "Y-Day" (Honshū, scheduled for March 1946).