Immediately after the Japanese attack on Pearl Harbor and the German declaration of war against the United States, as American and British military leaders met in Washington in a series of conferences known as Arcadia (December 1941-January 1942), they reaffirmed the ABC-1 decision to remain on the strategic defensive in the Pacific while defeating Germany first. They decided to wear down German resistance in 1942 by air bombardment, by assisting the USSR, and by trying to gain the entire North African coast, before initiating in 1943 a large-scale land offensive against Germany across either the Mediterranean Sea or the English channel. They also created the Combined Chiefs of Staff (CCS ), consisting of the United States Joint Chiefs of Staff and the British Chiefs of Staff, as the body to assist and advise President Franklin D. Roosevelt and Prime Minister Winston Churchill on the direction and conduct of the war. The most prominent members of the CCS were Gen. (later General of the Army) George C. Marshall, United States Army chief of staff, and Gen. (later Field Marshal) Sir Alan F. Brooke (later 1st Viscount Alanbrooke), chief of the Imperial General Staff. Because the CCS met only periodically, the American and British members did the detailed work of planning separately. Those most concerned with planning a European invasion were the Operations Division (OPD) of the United States War Department and the British Combined Commanders (the senior ground, naval, and air officers, together with Lord Mountbatten).
Differences between the Allies in general strategic outlook soon became apparent. The British, acutely conscious of the difficulty of a Channel crossing, aware of the need for special boats and equipment, and impressed by the strength of the German Army, favored a peripheral strategy, including ground operations in the Mediterranean or in Scandinavia and such indirect methods of attack as blockade, air bombardment, and the encouragement of subversive activities in German-occupied countries. Only when the Germans had been weakened to the point where an invasion would be sure of success was a cross-Channel attack to be launched. The Americans, more conscious of the needs of the Pacific war, and therefore impatient for victory in Europe, rejected the peripheral areas for major operations, for they believed that only by a showdown in northwestern Europe could the Germans be beaten.
As the first American ground troops (34th Division) arrived in Northern Ireland- in January 1942, the Special Observer Group was redesignated the United States Army Forces in the British Isles. Not long afterward, United States air force contingents began to arrive in England for eventual participation in the bombardment of German-held Europe, and in July American air crews in borrowed Royal Air Force (RAF) planes flew their first mission, a daylight attack against German airfields in the Netherlands. Then, in August, the Eighth Air Force, commanded by Maj. Gen. (later Gen.) Carl Spaatz, carried out the first bombing of Europe by American pilots flying American planes.
Because the Americans still were building up their strength and because British resources were hardly sufficient to carry out a cross-Channel attack alone, the British chiefs concluded that no cross-Channel operation was feasible in 1942 unless Germany showed unmistakable signs of collapse. Even 1943 remained doubtful. In March 1942, the OPD nevertheless began work on an outline plan for a full-scale invasion of Europe in 1943. The following month, General Marshall and Harry Hopkins, confidential adviser to President Roosevelt, went to London to try to gain British acceptance of the idea. The British agreed not only with the concept but also with a War Department proposal, code named Bolero, for a great buildup of American forces in Britain, with approximately 1 million men to be equipped and trained to carry out air operations in 1942 and a major invasion of the Continent in 1943. To implement the decision, Maj. Gen. (later Lt. Gen.) John C. H. Lee arrived in the United Kingdom in May to activate the Services of Supply. On June 24, Maj. Gen. (later General of the Army) Dwight D. Eisenhower arrived to take command of the European Theater of Operations, United States Army (ETOUSA ),.
Approval of the 1943 invasion-landings on a wide front between Boulogne and Le Havre, or Roundup, as it was called-did not solve the problem of what to do in 1942. That summer, President Roosevelt became increasingly convinced of the need for active operations in the European area before the end of the year. The commencement of a new German offensive in the USSR in June and British reverses in North Africa had their effects on his thinking. Fortunately, two decisive naval victories over the Japanese in May and June (Coral Sea and Midway) relieved the immediate threat to Australia and made it possible for the United States to divert greater resources to Europe. Despite the recommendations of General Marshall and Adm. (later Admiral of the Fleet) Ernest J. King, United States chief of naval operations (both of whom considered a North African venture a dispersal of strength), Roosevelt accepted a British proposal to invade North Africa that year (Operation Torch). The CCS appointed Eisenhower to assume immediate control of the planning. The decision to invade North Africa placed the Bolero-Roundup concept in jeopardy. Though planning for an eventual cross-Channel operation continued, Torch absorbed almost the entire effort and attention of the Allies in the European area. The invasion on Nov. 8, 1942, and the subsequent campaign through the winter and spring drained men, materiel, and supplies from the American buildup in the British Isles.
Meanwhile, the British had executed two daring raids against the German-held French coast. In March 1942, specially trained troops called Commandos launched a hit-and-run foray against St.-Nazaire and destroyed submarine pens and other naval facilities. In August, a joint British and Canadian command, with 5,000 Canadians, 1,000 British, and 50 United States Rangers, raided Dieppe in a miniature invasion to test amphibious tactics and techniques. Involving the full use of combined arms and the mass landings of infantry and armor to seize a beachhead, the Dieppe operation was designed not to hold a beachhead but rather to test the ability of the newly developed LCT (landing craft, tank) to land tanks across beaches, to see whether it was possible to capture a port in a frontal assault, to scrutinize the organization of air forces for overhead cover and support, and to test the naval management of a considerable invasion fleet. Of the 6,100 troops embarked for Dieppe, about 2,500 returned, including about 1,000 who never landed. The others were killed or captured.