The earliest use of the term D-Day by any army that the
U.S. Army Center of Military History and the
Oxford English Dictionary have been able to find was during
World War I: its first recorded use was 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
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 U.S. Army
General Dwight David Eisenhower to delay until June 6 and
that date has been popularly referred to ever since by the short title "D-Day". 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 would have begun on "X-Day" (on
Kyūshū, scheduled for November 1945) and "Y-Day" (on
Honshū, scheduled for March 1946). ==References==