The primary source of combat experience to prepare for the Normandy Invasion was earlier amphibious operations in the European Theatre. Amphibious operations in 1942-1944 in Algeria, Sicily, Salerno in Southern Italy, Anzio in Central Italy and other operations gave the command structure of the European theatre confidence in their own methods. Some of the units involved in these campaigns, 1st Infantry Division in particular, were considered by ETO command to be experts in Amphibious warfare. Likewise, in the naval command Admiral Kirk aboard heavy cruiser USS Augusta was in command for the Algeria, Sicily and Normandy invasions.

Additionally, the British had considerable experience in amphibious operations, as well as local experience of the Channel. The American operations were very much planned jointly with British forces with the British having an equal and at times leading role in the planning and preparations.

While some ideas may have been exchanged with the Pacific Theatre, I am not aware of any important ideas pioneered in the Pacific and implemented at D-Day.

However, one can see different solutions to similar problems being implemented by theatre. In the Pacific the US Navy and Marine Corps developed Amtracks, Amphibious Tractors, to provide armored support. In the European Theatre, this role was filled by DD tanks, regular tanks equipped with canvas flotation screens and a propeller drive.