On May 18, 1943, Roosevelt and Churchill sat down in Washington and picked a date for D-Day.
They chose May 1944. They missed by five weeks, mostly because of weather in the Channel. The largest amphibious invasion in human history was scheduled over cocktails, a year in advance, in a room overlooking the Potomac.
Churchill stayed at the White House for two weeks. He worked in a bathrobe. He required a martini before lunch and brandy after dinner. FDR's staff complained that he wandered the halls at 2am wanting to talk strategy. Roosevelt loved it.
The two men also agreed on the strategic bombing of Germany, the invasion of Italy, and the broad shape of the Pacific war. Stalin was not invited. He was told the decisions afterward.
Three of the most important years in modern history were drafted that fortnight.