The Build-up at the Port of Southampton before D-Day, 1944 Operation Overlord, launched on D-Day - 6th June 1944 - was the largest military invasion in history, with 156,000 troops landing on the Normandy beaches on the first day alone. Planning for the invasion of Europe began as early as autumn 1940 when the War Office surveyed the Southampton area with a view to using it as a base for a future invasion. The actual build-up began in the spring of 1942 when the Southampton area was designated a