One complication was the tidal flow in the English Channel, where high water moves from west to east, with high water at Lyme Regis occurring around six hours before it reaches Dover. If all the landings were to be made at high water across a broad front, they would have to be made at different times along different parts of the coast, with the landings in Dover being made six hours after any landings in Dorset and thus losing the element of surprise. If the landings were to be made at the same time, methods would have to be devised to disembark men, vehicles and supplies at all states of the tide. That was another reason to favour landing craft.