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, large-scale 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. While the ground forces were being equipped and trained the Allied air forces bombed the fortress of Europe. The Royal Air Force Bomber Command carried out the air assault by night and the United States Eighth Air Force by day. The first U. S. participation in the bombing of Europe from British bases was on 4 July 1942, when American crews flew six British bombers. During the fall of 1942 the Eighth Air Force prepared the Twelfth Air Force for the invasion of Africa, and it was not until the beginning of 1943 that U. S. bombers began to attack Europe from England in large-scale raids. From that time on the attacks on Germany continued with increasing intensity and shattering power until, in February 1944, the German Luftwaffe attempted to sweep the U. S. bombers from the skies over Europe. After a battle of one week’s duration over important industrial cities of Germany, the Luftwaffe was beaten and supremacy of the air was in Allied hands where it remained until the end of the war. [Illustration: NORTHERN IRELAND