One of the major challenges facing the D - Day landings was to secure a European port for the delivery of essential supplies .
Instead of capturing an existing port , the Allies decided on an audacious plan to build temporary harbours off the coast of Normandy .
One of the major challenges facing the D - Day landings was to secure a European port for the delivery of essential supplies , but instead of capturing an existing port , the Allies decided on an audacious plan to build temporary harbours off the coast of Normandy .