That the invasion would be launched from Britain
seemed obvious, once a plan to attack from the Mediterranean
had been dropped, but where exactly should the invasion
force land? It had to be somewhere with a suitable
shoreline, within easy reach of fighter cover from
British airfields and adjacent to ports that could
be used to maintain supplies.
The area between Calais and Boulogne was favoured
because the sea route was shortest, but the planners
also looked at the Belgian coastline and the bay of
the river Seine, in the west. This last was finally
accepted in June 1943.
The question of when the invasion should take place
was subject to all sorts of considerations but a tentative
date of May 1944 had been agreed in May 1943, subject
to the proviso that, if the situation on the Continent
changed dramatically before then, a force of some
sort must be available to intervene.