The Allies were reasonably confident that they would be successful in securing a foothold on the Normandy beachhead. The great concern was supplying the armies to advance across western Europe in a drive to Germany. Until great ports like Antwerp could be secured, the majority of the logistics would have to be delivered over the beaches. One of the most cumbersome commodities to deliver in war is fuel. The British, and most certainly the American armies were motorized and mechanized to a level never before seen in warfare, and every truck, tank, jeep and other impedimentia ran on gasoline, or as our British cousins called it, petrol.
The British gave much thought (and great effort) to the problems of logistics in the Normandy invasion, with many well known efforts, such as the famous Mulberry artificial harbors. One effort less well known was PLUTO, the Pipeline Under The Ocean, a series of pipelines laid across the English Channel to deliver bulk supplies of petrol ashore in France.
Mushdogs tipped me to this very interesting video showing just how complicated such a seemingly simple task was, involving fabricating a welded pipline 82 miles long, and then rolling it up like a spool of thread!