The Diver Plan was prepared in early 1944 following the first reports of the weapon in April 1943 and the discovery of its intended launch sites in late 1943. The plan had to be flexible enough to cover the anticipated assault on Britain and the needs of Operation Overlord, the Allied invasion of Europe. The V-1 offensive began on the sixth day after the D-Day landings on the beaches of Normandy, with the message "Diver, Diver, Diver".