In 1943 no principle existed within the U.S. Army for assaulting a heavily fortified coastline, and the only published advice in a U.S. Army Field Manual was that assaulting troops should avoid such defences and take them from the rear !
This was a unique problem for the U.S. Army who only had experience in the E.T.O. of amphibious assaults on defended coastlines in North Africa and Sicily.
Lieutenant Colonel Paul W. Thompson - an Engineer was assigned the mission to come up with a doctrine, and then train troops to successfully mount an assault on the north western coastline of Europe.
Beginning with nothing - he called a month-long conference in London in May 1943, seconding military experts from every service to thrash out a workable method of neutralising the German beach defences in western Europe. He called on experimental projects, collected vast amounts of data and photographs, and drew upon the combat experience of veterans of similar amphibious landings, including the raid on Dieppe.
Every aspect of the problem was considered, especially the terrain and topography to be encountered on the Normandy beaches selected for the American assault. This was probably the most crucial element that dictated the whole doctrine, for unlike the British and Canadian assaults destined to cross sandy beaches onto undulating grasslands, the Americans would immediately be faced with steep bluffs and only a few narrow valleys leading off the beach onto the plateau above on “Omaha”. Or, narrow causeways that had to be secured by infantry before any vehicles could move off the beach at “Utah”.
While the British and Candians could therefore immediately use their tanks, the Americans had to seize the valleys leading off the beach first, leaving them no alternative but to attack the defences with infantry, and land their tanks once access off the beach had been secured.
So - the assault had to be made by specially equipped and trained infantry sections as direct fire could not be depended upon to reduce pillboxes, and normal infantry weapons were powerless against concrete. Therefore beach defences had to be blown by hand placed charges set by self-contained thirty-man "Assault Sections" . These didn't exist in conventional infantry divisions, and demanded re-structuring.
Training therefore had to be based upon several assumptions including pillboxes and gun emplacements neutralised by flat trajectory, high velocity gunfire. Naval firepower was expected to provide this, but confidence in this eventuality gradually waned with training experience and alternative methods of delivering this initial barrage were explored and integrated into the American assault plan for D-Day. Tanks and artillery firing from landing craft as they approached the shore was one idea adopted, backed up by a small force of DD Tanks landing with the first waves on infantry and engineers.
