There were a number of factors in selecting landing beaches for Overlord. Firstly they had to be within range of UK-based fighter cover to ensure air superiority, broadly giving an area from Cherbourg to Flushing, ruling out Denmark. From a naval perspective operations in the English Channel (between Cherbourg and Calais) were desirable, limiting the dangers from German naval forces and requirement for minesweeping. Logistical considerations required the beaches be capable of maintaining the initial assault force, so sheltered if possible, with suitable terrain for moving supplies forward after the landings. Studying the beaches from Cherbourg to Flushing, the Dutch beaches were considered unsuitable due to limited road exits, an insufficient tide range for "drying out" (grounding a ship at high tide and unloading onto dry sand as the tide goes out) and exposure to prevailing winds. The Belgian beaches were also exposed to prevailing winds and strong currents, and backed by extensive sand dunes. Combined with the increased difficulties in naval operations east of Calais, the logical choices were therefore either the Pas de Calais or the Cotentin-Caen area. The former had the advantage of being the closest point to the UK, but as a result was the most heavily defended by the Germans, hence the selection of the latter.