Eisenhower and his high command were obsessed with ports. Only a large, fully operating port could satisfy supply needs, or so Eisenhower assumed. Therefore the planning emphasis had been on Cherbourg, and Le Havre next, with the climax coming at Antwerp. Only with these ports in operation could Eisenhower be assured of the supplies a final fifty-division offensive into Germany would require. Especially Antwerp.

The Germans assumed that the Allies could not supply divisions in combat over an open beach. The Allies tended to agree. Experience had not been encouraging. Churchill was so certain it couldn't be done he insisted on putting a very large share of the national effort into building two experimental artificial harbours. The harbours were moderately successful: their contribution to the total tonnage unloaded over the Normandy beaches was about fifteen per cent.

But as it turned out, it was the LSTs (landing ship tank), supported by the myriad of specialized landing craft, that did the most carrying and unloading LSTs at every beach, their great jaws yawning open, disgorging tanks and trucks and jeeps and bulldozers and guns and mountains of rations and ammunition, thousands of jerry cans filled with gasoline, crates of radios and telephones, typewriters, and forms, and all else that men at war require. The LSTs did what no one had thought possible. The LST was in fact the Allies' secret weapon.

Through June the Germans continued in the face of all evidence to believe LSTs could not supply the Allied divisions already ashore, and therefore Operation Overlord was a feint, with the real attack scheduled for the Pas-de-Calais later in the summer. A continuing campaign of misinformation put out by SHAEF reinforced this German fixed idea. So through the month, Hitler kept his panzer divisions north and east of the Seine River.