The build-up of the United States Army in the United Kingdom, from January 1942 until June 1944, with the huge amounts of supplies necessary to equip and maintain the forces and to prepare for the invasion of northern Europe was a tremendous undertaking. It involved the transportation of men and supplies across the Atlantic during a time when the German submarine menace was at its peak. The United States Navy played a vital role in transporting men and supplies and in protecting the convoys while en route. During this period the administrative task was enormous since facilities for quartering and training such large forces and for storing supplies and equipment had to be provided within the limited area of the United Kingdom. In October 1942 some of the units stationed in the United Kingdom were sent to the Mediterranean for the invasion of North Africa. The build-up continued after this, well-trained units arriving from the United States. As the time for the invasion of France approached, battle-tested units from the Mediterranean theater were transferred to England to prepare for their part in the assault. In spite of the limited terrain available, largescale maneuvers and realistic amphibious operations were conducted. In the early spring of 1944 joint exercises of the ground, sea, and air forces which were to make the attack in Normandy were held along the southern coast of England. The last of these exercises was held in early May, the units then moving to the staging areas and embarkation points for the invasion.