US AND EUROPE BEFORE THE US ENTRY INTO WWII
During the first two years of World War II, the United States maintained formal neutrality as made officially in the 1937 Quarantine Speech delivered by President Franklin D. Roosevelt on 5 October 1937 in Chicago, while supplying Britain, the Soviet Union, and China with war materials through the Lend-Lease Act (1941). In July 1941, still before the formal entry into the war, Britain passed responsibility for Iceland (despite being a neutral state, Iceland was invaded and occupied by the British in May 1940 as a measure to prevent German military presence there) to the United States under a US-Icelandic defense agreement. Roosevelt ordered the American occupation of Iceland on June 16, 1941 and the U.S. troops remained there for the duration of the war.
In the 29 March 1941 report of the ABC-1 conference, the Americans and British agreed on their strategic objectives. These included the defeat of Germany with the principal military effort of the United States in the Atlantic and Europe and a strategic defense in the Far East. The resulting strategy known as "Europe first" presumed that the US and the UK would use the preponderance of their resources to subdue Nazi Germany in Europe first. They would also fight a holding action against Japan in the Pacific, using fewer resources. After the defeat of Germany—considered the greatest threat to Great Britain—all Allied forces could be concentrated against Japan. Despite the diplomatic assurances that Germany was "the prime enemy" in the war, official U.S. statistics show that the United States devoted more resources in the early part of the war to stopping the advance of Japan, and not until 1944 was a clear preponderance of U.S. resources allocated toward the defeat of Germany.
The United States also supported the Allies in Europe during the Battle of Atlantic (1939-1945) prior to its official entry into the war. From September 1941, convoys, coming mainly from North America and predominantly going to the United Kingdom and the Soviet Union, were protected for the most part by the British and Canadian navies and air forces aided by ships and aircraft of the United States.
FORMAL ENTRY INTO THE EUROPEAN THEATER
The United States entered the war in the west with Operation Torch in North Africa on 8 November 1942 although in mid-1942, the US Army Air Forces (USAAF) arrived in the UK and carried out a few raids across the English Channel. In 1943, the US participated in the Allies' invasion of Sicily and Italy. In July, the American seaborne assault landed on the southern coast of Sicily and units of an airborne division parachuted ahead of landings. On August 11, seeing that the battle was lost, the German and Italian commanders began evacuating their forces from Sicily to Italy. On 17 August, the Allies were in control of the island.
The first Allied troops landed on the Italian peninsula on 3 September 1943 and Italy surrendered on September 8 (although Mussolini's Italian Social Republic was established soon afterwards). The first American troops landed at Salerno on September 9, 1943. The Germans launched fierce counterattacks. The US 5th Army and other Allied armies broke through two German defensive lines (Volturno and the Barbara Line) in October and November 1943. After heavy winter and challenges that it posed to the Allies, Rome fell on June 4, 1944. Following the Normandy invasion in June 1944, the equivalent of seven US and French divisions were pulled out of Italy to Participate in Operation Dragoon: the allied landings in southern France. Despite this the remaining US forces in Italy with other Allied forces pushed up to the last major defensive line in Northern Italy. The Italian Campaign ended on May 2, 1945 and US forces in mainland Italy suffered between 114,000 and over 119,000 casualties.
From 1942, numerous bombing runs were launched by the United States aimed at the industrial heart of Germany. In January 1943, at the Casablanca Conference, it was agreed Royal Air Force (RAF) Bomber Command operations against Germany would be reinforced by the USAAF in a Combined Operations Offensive plan called Operation Pointblank. At the beginning of the combined strategic bombing offensive on 4 March 1943, 669 RAF and 303 USAAF heavy bombers were available.
In the later stage of the war, the United States was heavily involved in the Operation Overlord (the code name for the Battle of Normandy) - the Allied operation that launched the successful invasion of German-occupied Western Europe. It commenced on June 6, 1944 with the Normandy landings (Operation Neptune, commonly known as D-Day). General Dwight D. Eisenhower was appointed commander of Supreme Headquarters Allied Expeditionary Force (SHAEF), and British General Bernard Montgomery was named as commander of the 21st Army Group, which comprised all the land forces involved in the invasion. In the months leading up to the invasion, the Allies conducted a substantial military deception, Operation Bodyguard, using both electronic and visual misinformation. This misled the Germans as to the date and location of the main Allied landings.
Key American military officials in Europe, Office of War Information, 1945
Senior American commanders of World War II in Europe. Seated are (from left to right) Gens. William H. Simpson, George S. Patton, Carl A. Spaatz, Dwight D. Eisenhower, Omar Bradley, Courtney H. Hodges, and Leonard T. Gerow; standing are (from left to right) Gens. Ralph F. Stearley, Hoyt Vandenberg, Walter Bedell Smith, Otto P. Weyland, and Richard E. Nugent.