Military history of the United States during World War II

The military history of the United States during World War II covers the victorious Allied war against the Axis Powers, starting with the 7 December 1941 attack on Pearl Harbor and ending with the 2 September 1945 surrender of Japan. During the first two years of World War II, the United States had maintained formal neutrality which was made official in the Quarantine Speech which was delivered by US President Franklin D. Roosevelt in 1937, while it was supplying Britain, the Soviet Union, and China with war materiel through the Lend-Lease Act which was signed into law on 11 March 1941, as well as deploying the US military to replace the British forces stationed in Iceland. Following the " Greer incident" Roosevelt publicly confirmed the "shoot on sight" order on 11 September 1941, effectively declaring naval war on Germany and Italy in the Battle of the Atlantic. In the Pacific Theater, there was unofficial early US combat activity such as the Flying Tigers.

During the war, some 16,112,566 Americans served in the United States Armed Forces, with 405,399 killed and 671,278 wounded. There were also 130,201 American prisoners of war, of whom 116,129 returned home after the war. Key civilian advisors to President Roosevelt included Secretary of War Henry L. Stimson, who mobilized the nation's industries and induction centers to supply the Army, commanded by General George Marshall and the Army Air Forces under General Hap Arnold. The Navy, led by Secretary of the Navy Frank Knox and Admiral Ernest King, proved more autonomous. Overall priorities were set by Roosevelt and the Joint Chiefs of Staff, chaired by William Leahy. The highest priority was the defeat of Germany in Europe, but first the war against Japan in the Pacific was more urgent after the sinking of the main battleship fleet at Pearl Harbor.

Admiral King put Admiral Chester W. Nimitz, based in Hawaii, in charge of the Pacific War against Japan. The Imperial Japanese Navy had the advantage, taking the Philippines as well as British and Dutch possessions, and threatening Australia but in June 1942, its main carriers were sunk during the Battle of Midway, and the Americans seized the initiative. The Pacific War became one of island hopping, so as to move air bases closer and closer to Japan. The Army, based in Australia under General Douglas MacArthur, steadily advanced across New Guinea to the Philippines, with plans to invade the Japanese home islands in late 1945. With its merchant fleet sunk by American submarines, Japan ran short of aviation gasoline and fuel oil, as the US Navy in June 1944 captured islands within bombing range of the Japanese home islands. Strategic bombing directed by General Curtis Lemay destroyed all the major Japanese cities, as the US captured Okinawa after heavy losses in spring 1945. With the atomic bombings of Hiroshima and Nagasaki, the Soviet invasion of Manchuria, and an invasion of the home islands imminent, Japan surrendered.

The war in Europe involved aid to Britain, her allies, and the Soviet Union, with the US supplying munitions until it could ready an invasion force. US forces were first tested to a limited degree in the North African Campaign and then employed more significantly with British Forces in Italy in 1943–45, where US forces, representing about a third of the Allied forces deployed, bogged down after Italy surrendered and the Germans took over. Finally the main invasion of France took place in June 1944, under General Dwight D. Eisenhower. Meanwhile, the US Army Air Forces and the British Royal Air Force engaged in the area bombardment of German cities and systematically targeted German transportation links and synthetic oil plants, as it knocked out what was left of the Luftwaffe post Battle of Britain in 1945. Being invaded from all sides, it became clear that Germany would lose the war. Berlin fell to the Soviets in May 1945, and with Adolf Hitler dead, the Germans surrendered.

The American victorious military effort was strongly supported by civilians on the home front, who provided the military personnel, the munitions, the money, and the morale to fight the war to victory. World War II cost the United States an estimated $341 billion in 1945 dollars – equivalent to 74% of America's GDP and expenditures during the war. In 2020 dollars, the war cost over $4.9 trillion.

Origins

American public opinion was hostile to the Axis, but how much aid to give the Allies was controversial. The United States returned to its typical isolationist foreign policy after the First World War and President Woodrow Wilson's failure to have the Treaty of Versailles ratified. Although President Franklin D. Roosevelt personally favored a more assertive foreign policy, his administration remained committed to isolationism during the 1930s to ensure congressional support for the New Deal, and allowed Congress to pass the Neutrality Acts. As a result, the United States played no role in the Second Italo-Ethiopian War and the Spanish Civil War. After the German invasion of Poland and the beginning of the war in September 1939, Congress allowed foreign countries to purchase war materiel from the United States on a " cash-and-carry" basis, but assistance to the United Kingdom was still limited by British hard currency shortages and the Johnson Act, and President Roosevelt's military advisers believed that the Allied Powers would be defeated and that US military assets should be focused on defending the Western Hemisphere.

By 1940 the US, while still neutral, was becoming the " Arsenal of Democracy" for the Allies, supplying money and war materials. Prime Minister Winston Churchill and President Roosevelt agreed to exchange 50 US destroyers for 99-year-leases to British military bases in Newfoundland and the Caribbean. The sudden defeat of France in spring 1940 caused the nation to begin to expand its armed forces, including the first peacetime draft. In preparation for expected German aggression against the Soviet Union, negotiations for better diplomatic relations began between Undersecretary of State Sumner Welles and Soviet Ambassador to the United States Konstantin Umansky. After the German invasion of the Soviet Union in June 1941, America began sending Lend Lease aid to the Soviet Union as well as Britain and China. Although President Franklin D. Roosevelt's advisers warned that the Soviet Union would collapse from the Nazi advance within weeks, he barred Congress from blocking aid to the Soviet Union on the advice of Harry Hopkins. In August 1941, President Roosevelt and Prime Minister Churchill met aboard the ''USS Augusta'' at Naval Station Argentia in Placentia Bay, Newfoundland, and produced the Atlantic Charter outlining mutual aims for a postwar liberalized international system.

Public opinion was even more hostile to Japan, and there was little opposition to increased support for China. After the 1931 Japanese invasion of Manchuria, the United States articulated the Stimson Doctrine, named for Secretary of State Henry L. Stimson, stating that no territory conquered by military force would be recognized. The United States also withdrew from the Washington Naval Treaty limiting naval tonnage in response to Japan's violations of the Nine-Power Treaty and the Kellogg–Briand Pact. Public opposition to Japanese expansionism in Asia had mounted during the Second Sino-Japanese War when the Imperial Japanese Army Air Service attacked and sank the US Yangtze Patrol gunboat in the Yangtze River while the ship was evacuating civilians from the Nanjing Massacre''.'' Although the US government accepted Japanese official apologies and indemnities for the incident, it resulted in increasing trade restrictions against Japan and corresponding increases US credit and aid to China. After the United States abrogated the 1911 Treaty of Commerce and Navigation with Japan, Japan ratified the Tripartite Pact and embarked on an invasion of French Indochina. The United States responded by placing a complete embargo on Japan through the Export Control Act of 1940, freezing Japanese bank accounts, halting negotiations with Japanese diplomats, and supplying China through the Burma Road.

American volunteers

Before America entered World War II in December 1941, individual Americans volunteered to fight against the Axis powers in other nations' armed forces. Although under American law, it was illegal for United States citizens to join the armed forces of foreign nations, and in doing so, they lost their citizenship, many American volunteers changed their nationality to Canadian. However, Congress passed a blanket pardon in 1944. American mercenary Colonel Charles Sweeny began recruiting American citizens to fight as a US volunteer detachment in the French Air Force, however France fell before this was implemented. During the Battle of Britain, 11 American pilots flew in the Royal Air Force. Charles Sweeney's nephew, also named Charles, formed a Home Guard unit from American volunteers living in London.

One notable example was the Eagle Squadrons, which were RAF squadrons made up of American volunteers and British personnel. The first to be formed was No. 71 Squadron on 19 September 1940, followed by No. 121 Squadron on 14 May 1941 and No. 133 Squadron on 1 August 1941. 6,700 Americans applied to join but only 244 got to serve with the three Eagle squadrons; 16 Britons also served as squadron and flight commanders. The first became operational in February 1941 and the squadrons scored their first kill in July 1941. On 29 September 1942, the three squadrons were officially turned over by the RAF to the Eighth Air Force of the US Army Air Forces and became the 4th Fighter Group. In their time with the RAF the squadrons claim to have shot 73½ German planes; 77 Americans and 5 Britons were killed.

Another notable example was the Flying Tigers, created by Claire L. Chennault, a retired US Army Air Corps officer working in the Republic of China since August 1937, first as military aviation advisor to Generalissimo Chiang Kai-shek in the early months of the Sino-Japanese War. Officially known as the 1st American Volunteer Group (AVG) but nicknamed the "Flying Tigers", this was a group of American pilots already serving in the US Armed forces and recruited under presidential authority. As a unit they served in the Chinese Air Force against the Japanese. The group comprised three fighter squadrons of around 30 aircraft each. The AVG's first combat mission was on 20 December 1941, twelve days after the Pearl Harbor attack. On 4 July 1942 the AVG was disbanded, and was replaced by the 23rd Fighter Group of the United States Army Air Forces, which was later absorbed into the US Fourteenth Air Force. During their time in the Chinese Air Force, they succeeded in destroying 296 enemy aircraft,Ford 1991, pp. 30–34. while losing only 14 pilots in combat.

Command system

In 1942 President Franklin D. Roosevelt set up a new command structure to provide leadership in the US Armed Forces while retaining authority as Commander-in-Chief as assisted by Secretary of War Henry Stimson with Admiral Ernest J. King as Chief of Naval Operations in complete control of the Navy and of the Marine Corps through its Commandant, then Lt. General Thomas Holcomb and his successor as Commandant of the Marine Corps, Lt. General Alexander Vandegrift, General George C. Marshall in charge of the Army, and in nominal control of the Air Force, which in practice was commanded by General Hap Arnold on Marshall's behalf. King was also in control for wartime being of the US Coast Guard under its Commandant, Admiral Russell R. Waesche. Roosevelt formed a new body, the Joint Chiefs of Staff, which made the final decisions on American military strategy and as the chief policy-making body for the armed forces. The Joint Chiefs was a White House agency chaired by Admiral William D. Leahy, who became FDR's chief military advisor and the highest military officer of the US at that time.

As the war progressed Marshall became the dominant voice in the JCS in the shaping of strategy. When dealing with Europe, the Joint Chiefs met with their British counterparts and formed the Combined Chiefs of Staff. Unlike the political leaders of the other major powers, Roosevelt rarely overrode his military advisors. The civilians handled the draft and procurement of men and equipment, but no civilians—not even the secretaries of War or Navy, had a voice in strategy. Roosevelt avoided the State Department and conducted high-level diplomacy through his aides, especially Harry Hopkins. Since Hopkins also controlled $50 billion in Lend Lease funds given to the Allies, they paid attention to him.

Lend-Lease and Iceland Occupation

The year 1940 marked a change in attitude in the United States. The German victories in France, Poland and elsewhere, combined with the Battle of Britain, led many Americans to believe that some intervention would be needed. In March 1941, the Lend-Lease program began shipping money, munitions, and food to Britain, China, and (by that fall) the Soviet Union.

By 1941 the United States was taking an active part in the war, despite its nominal neutrality. In spring U-boats began their "wolf-pack" tactics which threatened to sever the trans- Atlantic supply line; Roosevelt extended the Pan-American Security Zone east almost as far as Iceland. The US Navy's "neutrality patrols" were not actually neutral as, in practice, their function was to report Axis ship and submarine sightings to the British and Canadian navies, and from April the US Navy began escorting Allied convoys from Canada as far as the "Mid-Atlantic Meeting Point" (MOMP) south of Iceland, where they handed off to the RN.

On 16 June 1941, after negotiation with Churchill, Roosevelt ordered the United States occupation of Iceland to replace the British invasion forces. On 22 June 1941, the US Navy sent Task Force 19 (TF 19) from Charleston, South Carolina to assemble at Argentia, Newfoundland. TF 19 included 25 warships and the 1st Provisional Marine Brigade of 194 officers and 3714 men from San Diego, California under the command of Brigadier General John Marston. Task Force 19 (TF 19) sailed from Argentia on 1 July. On 7 July, Britain persuaded the Althing to approve an American occupation force under a US-Icelandic defense agreement, and TF 19 anchored off Reykjavík that evening. US Marines commenced landing on 8 July, and disembarkation was completed on 12 July. On 6 August, the US Navy established an air base at Reykjavík with the arrival of Patrol Squadron VP-73 PBY Catalinas and VP-74 PBM Mariners. US Army personnel began arriving in Iceland in August, and the Marines had been transferred to the Pacific by March 1942. Up to 40,000 US military personnel were stationed on the island, outnumbering adult Icelandic men (at the time, Iceland had a population of about 120,000.) The agreement was for the US military to remain until the end of the war (although the US military presence in Iceland remained through 2006, as postwar Iceland became a member of NATO).

American warships escorting Allied convoys in the western Atlantic had several hostile encounters with U-boats. On 4 September, a German U-Boat attacked the destroyer off Iceland. A week later Roosevelt ordered American warships to attack U-boats on sight. A U-boat shot up the as it escorted a British merchant convoy. The was sunk by on 31 October 1941.

European and North African Theaters

On 11 December 1941, three days after the United States declared war on Japan, Adolf Hitler and Nazi Germany declared war against the United States. That same day, the United States declared war on Germany and Italy.

Europe first

The established grand strategy of the Allies was to defeat Germany and its allies in Europe first, and then focus could shift towards Japan in the Pacific. This was because two of the Allied capitals, London and Moscow, could be directly threatened by Germany, but none of the major Allied capitals were threatened by Japan.
Germany was the United Kingdom's primary threat, especially after the Fall of France in 1940, which saw Germany overrun most of the countries of Western Europe, leaving the United Kingdom alone to combat Germany. Germany's planned invasion of the UK, Operation Sea Lion, was averted by its failure to establish air superiority in the Battle of Britain. At the same time, war with Japan in East Asia seemed increasingly likely. Although the US was not yet at war with either Germany or Japan, it met with the UK on several occasions to formulate joint strategies.

In the 29 March 1941 report of the ABC-1 conference, the Americans and British agreed that their strategic objectives were: (1) "The early defeat of Germany as the predominant member of the Axis with the principal military effort of the United States being exerted in the Atlantic and European area; and (2) A strategic defensive in the Far East."
Thus, the Americans concurred with the British in the grand strategy of "Europe first" (or "Germany first") in carrying out military operations in World War II. The UK feared that, if the United States was diverted from its main focus in Europe to the Pacific (Japan), Hitler might crush both the Soviet Union and Britain, and would then become an unconquerable fortress in Europe. The wound inflicted on the United States by Japan at Pearl Harbor on 7 December 1941, did not result in a change in US policy. Prime Minister Winston Churchill hastened to Washington shortly after Pearl Harbor for the Arcadia Conference to ensure that the Americans didn't have second thoughts about Europe First. The two countries reaffirmed that, "notwithstanding the entry of Japan into the War, our view remains that Germany is still the prime enemy. And her defeat is the key to victory. Once Germany is defeated the collapse of Italy and the defeat of Japan must follow."

Battle of the Atlantic

The Battle of the Atlantic was the longest continuous military campaign in World War II, running from 1939 to the defeat of Germany in 1945. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. It was at its height from mid-1940 through to the end of 1943. The Battle of the Atlantic pitted U-boats and other warships of the Kriegsmarine (German navy) and aircraft of the Luftwaffe (German Air Force) against the Royal Canadian Navy, Royal Navy, the United States Navy, and Allied merchant shipping. The 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. These forces were aided by ships and aircraft of the United States from 13 September 1941. The Germans were joined by submarines of the Italian Royal Navy (Regia Marina) after their Axis ally Italy entered the war on 10 June 1940.

Operation Torch

The United States entered the war in the west with Operation Torch on 8 November 1942, after their Soviet allies had pushed for a second front against the Germans. General Dwight Eisenhower commanded the assault on North Africa, and Major General George Patton struck at Casablanca.

Allied victory in North Africa

The United States did not have a smooth entry into the war against Nazi Germany. Early in 1943, the United States Army suffered a near-disastrous defeat at the Battle of the Kasserine Pass in February. The senior Allied leadership was primarily to blame for the loss as internal bickering between American General Lloyd Fredendall and the British led to mistrust and little communication, causing inadequate troop placements. The defeat could be considered a major turning point, however, because General Eisenhower replaced Fredendall with General Patton.

Slowly the Allies stopped the German advance in Tunisia and by March were pushing back. In mid-April, under British General Bernard Montgomery, the Allies smashed through the Mareth Line and broke the Axis defense in North Africa. On 13 May 1943, Axis troops in North Africa surrendered, leaving behind 275,000 men. Allied efforts turned towards Sicily and Italy.

Invasion of Sicily and Italy

The first stepping stone for the Allied liberation of Europe was invading Europe through Italy. Launched on 9 July 1943, Operation Husky was, at the time, the largest amphibious operation ever undertaken. The American seaborne assault by the US 7th Army landed on the southern coast of Sicily between the town of Licata in the west, and Scoglitti in the east and units of the 82nd airborne division parachuted ahead of landings. Despite the elements, the operation was a success and the Allies immediately began exploiting their gains. On 11 August, 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, US 7th Army lost 8,781 men (2,237 killed or missing, 5,946 wounded, and 598 captured).

Following the Allied victory in Sicily, Italian public sentiment swung against the war and Italian dictator Benito Mussolini. He was dismissed from office by the Fascist Grand Council and King Victor Emmanuel III, and the Allies struck quickly, hoping resistance would be slight. The first Allied troops landed on the Italian peninsula on 3 September 1943 and Italy surrendered on 8 September, however the Italian Social Republic was established soon afterwards. The first American troops landed at Salerno on 9 September 1943, by U.S. Fifth Army. However, German troops in Italy were prepared, and after the Allied troops at Salerno had consolidated their beachhead, the Germans launched fierce counterattacks. However, they failed to destroy the beachhead and retreated on 16 September and in October 1943 began preparing a series of defensive lines across central Italy. The US 5th Army and other Allied armies broke through the first two lines (Volturno and the Barbara Line) in October and November 1943. As winter approached, the Allies made slow progress due to the weather and the difficult terrain against the heavily defended German Winter Line; they did however manage to break through the Bernhardt Line in January 1944. By early 1944 the Allied attention had turned to the western front and the Allies were taking heavy losses trying to break through the Winter Line at Monte Cassino. The Allies landed at Anzio on 22 January 1944 to outflank the Gustav line and pull Axis forces out of it so other allied armies could breakthrough. After slow progress, the Germans counterattacked in February but failed to stamp out the Allies; after months of stalemate, the Allies broke out in May 1944 and Rome fell to the Allies on 4 June 1944.

Following the Normandy invasion on 6 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 Gothic line in northern Italy, the last major defensive line. From August 1944 to March 1945 the Allies managed to breach the formidable defenses but they narrowly failed to break out into the Lombardy Plains before the winter weather closed in and made further progress impossible. In April 1945 the Allies broke through the remaining Axis positions in Operation Grapeshot ending the Italian Campaign on 2 May 1945; US forces in mainland Italy suffered between 114,000 and over 119,000 casualties.

Strategic bombing

Numerous bombing runs were launched by the United States aimed at the industrial heart of Germany. Using the high altitude B-17 and B-24, the raids had to be conducted in daylight for the drops to be accurate. As adequate fighter escort was rarely available, the bombers would fly in tight, box formations, allowing each bomber to provide overlapping machine-gun fire for defense. The tight formations made it impossible to evade fire from '' Luftwaffe'' fighters, however, and American bomber crew losses were high. One such example was the Schweinfurt-Regensburg mission, which resulted in staggering losses of men and equipment. The introduction of the revered P-51 Mustang, which had enough fuel to make a round trip to Germany's heartland, helped to reduce losses later in the war.

In mid-1942, the United States Army Air Forces (USAAF) arrived in the UK and carried out a few raids across the English Channel. The USAAF Eighth Air Force's B-17 bombers were called the "Flying Fortresses" because of their heavy defensive armament of ten to twelve machine guns, and armor plating in vital locations. In part because of their heavier armament and armor, they carried smaller bomb loads than British bombers. With all of this, the USAAF's commanders in Washington, DC, and in Great Britain adopted the strategy of taking on the Luftwaffe head-on, in larger and larger air raids by mutually defending bombers, flying over Germany, Austria, and France at high altitudes during the daytime. Also, both the US Government and its Army Air Forces commanders were reluctant to bomb enemy cities and towns indiscriminately. They claimed that by using the B-17 and the Norden bombsight, the USAAF should be able to carry out "precision bombing" on locations vital to the German war machine: factories, naval bases, shipyards, railroad yards, railroad junctions, power plants, steel mills, airfields, etc.

In January 1943, at the Casablanca Conference, it was agreed RAF Bomber Command operations against Germany would be reinforced by the USAAF in a Combined Operations Offensive plan called Operation Pointblank. Chief of the British Air Staff MRAF Sir Charles Portal was put in charge of the "strategic direction" of both British and American bomber operations. The text of the Casablanca directive read: "Your primary object will be the progressive destruction and dislocation of the German military, industrial and economic system and the undermining of the morale of the German people to a point where their capacity for armed resistance is fatally weakened.", At the beginning of the combined strategic bombing offensive on 4 March 1943 669 RAF and 303 USAAF heavy bombers were available.

In late 1943, 'Pointblank' attacks manifested themselves in the infamous Schweinfurt raids (first and second). Formations of unescorted bombers were no match for German fighters, which inflicted a deadly toll. In despair, the Eighth halted air operations over Germany until a long-range fighter could be found in 1944; it proved to be the P-51 Mustang, which had the range to fly to Berlin and back.

USAAF leaders firmly held to the claim of "precision bombing" of military targets for much of the war, and dismissed claims they were simply bombing cities. However, the American Eighth Air Force received the first H2X radar sets in December 1943. Within two weeks of the arrival of these first six sets, the Eighth command permitted them to area bomb a city using H2X and would continue to authorize, on average, about one such attack a week until the end of the war in Europe.

In reality, the day bombing was "precision bombing" only in the sense that most bombs fell somewhere near a specific designated target such as a railway yard. Conventionally, the air forces designated as "the target area" a circle having a radius of 1000 feet around the aiming point of attack. While accuracy improved during the war, Survey studies show that, overall, only about 20% of the bombs aimed at precision targets fell within this target area. In the fall of 1944, only seven percent of all bombs dropped by the Eighth Air Force hit within 1,000 feet of their aim point. The only offensive ordnance possessed by the USAAF that was guidable, the VB-1 Azon, saw very limited service in Europe and in the CBI Theater late in the war.

Nevertheless, the sheer tonnage of explosives delivered by day and by night was eventually enough to cause widespread damage, and, more importantly from a military point of view, forced Germany to divert resources to counter it. This was to be the real significance of the Allied strategic bombing campaign—resource allocation.

To improve USAAF fire bombing capabilities a mock-up German village was built and repeatedly burned down. It contained full-scale replicas of German homes. Fire bombing attacks proved successful, in a single 1943 attack on Hamburg about 50,000 civilians were killed and almost the entire city destroyed.

With the arrival of the brand-new Fifteenth Air Force, based in Italy, command of the US Air Forces in Europe was consolidated into the United States Strategic Air Forces (USSAF). With the addition of the Mustang to its strength, the Combined Bomber Offensive was resumed. Planners targeted the Luftwaffe in an operation known as ' Big Week' (20–25 February 1944) and succeeded brilliantly – losses were so heavy German planners were forced into a hasty dispersal of industry and the day fighter arm never fully recovered.

The dismissal of General Ira Eaker at the end of 1943 as commander of the Eighth Air Force and his replacement by an American aviation legend, Maj. Gen Jimmy Doolittle signaled a change in how the American bombing effort went forward over Europe. Doolittle's major influence on the European air war occurred early in the year when he changed the policy requiring escorting fighters to remain with the bombers at all times. With his permission, initially performed with P-38s and P-47s with both previous types being steadily replaced with the long-ranged P-51s as the spring of 1944 wore on, American fighter pilots on bomber defense missions would primarily be flying far ahead of the bombers' combat box formations in air supremacy mode, literally "clearing the skies" of any Luftwaffe fighter opposition heading towards the target. This strategy fatally disabled the twin-engined ''Zerstörergeschwader'' heavy fighter wings and their replacement, single-engined ''Sturmgruppen'' of heavily armed Fw 190As, clearing each force of bomber destroyers in their turn from Germany's skies throughout most of 1944. As part of this game-changing strategy, especially after the bombers had hit their targets, the USAAF's fighters were then free to strafe German airfields and transport while returning to base, contributing significantly to the achievement of air superiority by Allied air forces over Europe.

On 27 March 1944, the Combined Chiefs of Staff issued orders granting control of all the Allied air forces in Europe, including strategic bombers, to General Dwight D. Eisenhower, the Supreme Allied Commander, who delegated command to his deputy in SHAEF Air Chief Marshal Arthur Tedder. There was resistance to this order from some senior figures, including Winston Churchill, Harris, and Carl Spaatz, but after some debate, control passed to SHAEF on 1 April 1944. When the Combined Bomber Offensive officially ended on 1 April, Allied airmen were well on the way to achieving air superiority over all of Europe. While they continued some strategic bombing, the USAAF along with the RAF turned their attention to the tactical air battle in support of the Normandy Invasion. It was not until the middle of September that the strategic bombing campaign of Germany again became the priority for the USAAF.

The twin campaigns—the USAAF by day, the RAF by night—built up into massive bombing of German industrial areas, notably the Ruhr, followed by attacks directly on cities such as Hamburg, Kassel, Pforzheim, Mainz and the often-criticized bombing of Dresden.

Operation Overlord

The second European front that the Soviets had pressed for was finally opened on 6 June 1944, when the Allies launched an invasion of Normandy.
Supreme Allied Commander General Dwight D. Eisenhower had delayed the attack because of bad weather, but finally, the largest amphibious assault in history began.

After prolonged bombing runs on the French coast by the Army Air Forces, 225 US Army Rangers scaled the cliffs at Pointe du Hoc under intense enemy fire and destroyed the German gun emplacements that could have threatened the amphibious landings. Also before the main amphibious assault, the American 82nd and 101st Airborne divisions dropped behind the beaches into Nazi-occupied France, to protect the coming landings. Many of the paratroopers were not dropped on their intended landing zones and were scattered throughout Normandy.

As the paratroops fought their way through the hedgerows, the main amphibious landings began. The Americans came ashore at the beaches codenamed 'Omaha' and ' Utah'. The landing craft bound for Utah, as with so many other units, went off course, coming ashore two kilometers off target. The 4th Infantry Division faced weak resistance during the landings and by the afternoon were linked up with paratroopers fighting their way towards the coast.

At Omaha the Germans had prepared the beaches with land mines, Czech hedgehogs and Belgian Gates in anticipation of the invasion. Intelligence before the landings had placed the less experienced German 714th Division in charge of the defense of the beach. However, the highly trained and experienced 352nd moved in days before the invasion. As a result, the soldiers from the 1st and 29th Infantry Divisions became pinned down by superior enemy fire immediately after leaving their landing craft. In some instances, entire landing craft full of men were mowed down by the well-positioned German defenses. As the casualties mounted, the soldiers formed impromptu units and advanced inland.

The small units then fought their way through the minefields that were in between the Nazi machine-gun bunkers. After squeezing through, they then attacked the bunkers from the rear, allowing more men to come safely ashore.

By the end of the day, the Americans suffered over 6,000 casualties. Omaha Beach is the code name for one of the five sectors of the Allied invasion of German-occupied France in the Normandy landings on 6 June 1944, during World War II. The beach is on the coast of Normandy, France, facing the English Channel, and is long, from east of Sainte-Honorine-des-Pertes to west of Vierville-sur-Mer on the right bank of the Douve River estuary. Landings here were necessary to link up the British landings to the east at Gold Beach with the American landing to the west at Utah Beach, thus providing a continuous lodgement on the Normandy coast of the Bay of the Seine. Taking Omaha was to be the responsibility of United States Army troops, with sea transport and naval artillery support provided by the US Navy and elements of the British Royal Navy.

On D-Day, the untested 29th Infantry Division, joined by the veteran 1st Infantry Division and nine companies of US Army Rangers redirected from Pointe du Hoc, were to assault the western half of the beach. The battle-hardened 1st Infantry Division was given the eastern half. The initial assault waves, consisting of tanks, infantry, and combat engineer forces, were carefully planned to reduce the coastal defenses and allow the larger ships of the follow-up waves to land.

The primary objective at Omaha was to secure a beachhead of some five miles (eight kilometers) depth, between Port-en-Bessin and the Vire River, linking with the British landings at Gold Beach to the east, and reaching the area of Isigny to the west to link up with VII Corps landing at Utah Beach. Opposing the landings was the German 352nd Infantry Division, a large portion of whom were teenagers, though they were supplemented by veterans who had fought on the Eastern Front. The 352nd had never had any battalion or regimental training. Of the 12,020 men of the division, only 6,800 were experienced combat troops, detailed to defend a 53-kilometer-long (33-mile) front. The Germans were largely deployed in strongpoints along the coast—the German strategy was based on defeating any seaborne assault at the waterline. Nevertheless, Allied calculations indicated that Omaha's defenses were three times as strong as those they had encountered during the Battle of Kwajalein, and its defenders were four times as many.

Very little went as planned during the landing at Omaha Beach. Navigation difficulties caused the majority of landing craft to miss their targets throughout the day. The defenses were unexpectedly strong, and inflicted heavy casualties on landing US troops. Under heavy fire, the engineers struggled to clear the beach obstacles; later landings bunched up around the few channels that were cleared. Weakened by the casualties taken just in landing, the surviving assault troops could not clear the heavily defended exits off the beach. This caused further problems and consequent delays for later landings. Small penetrations were eventually achieved by groups of survivors making improvised assaults, scaling the bluffs between the most heavily defended points. By the end of the day, two small isolated footholds had been won, which were subsequently exploited against weaker defenses further inland, thus achieving the original D-Day objectives over the following days．

With the Beaches secured, the Allies needed to secure a deep-water port to allow reinforcements to be brought in, with American forces at the base of the Cotentin Peninsula the target was Cherbourg, at the end of the Cotentin. The US VII Corps immediately began making their push after the beaches were secured on 6 June, facing a mix of weak regiments and battlegroups from several divisions who used the bocage terrain, flooded fields and narrow roads to their advantage which slowed the American advance. After being reinforced, VII corps took control of the peninsula in fierce fighting on 19 June and launched their assault on Cherbourg on 22 June. The German garrison surrendered on 29 June, but by this time they had destroyed the port facilities, which were not made fully operational until September.

Battle of Saint-Lô

The Battle of Saint-Lô is one of the three conflicts in the Battle of the Hedgerows (fr), which took place between 9–24 July 1944, just before Operation Cobra. Saint-Lô had fallen to Germany in 1940, and, after the Invasion of Normandy, the Americans targeted the city, as it served as a strategic crossroads. American bombardments caused heavy damage (up to 95% of the city was destroyed) and a high number of casualties, which resulted in the martyr city being called "The Capital of Ruins", popularized in a report by Samuel Beckett

Battle of Carentan

The Battle of Carentan was an engagement between airborne forces of the United States Army and the German Wehrmacht during the Battle of Normandy. The battle took place between 10 and 15 June 1944, on the approaches to and within the city of Carentan, France.

The objective of the attacking American forces was the consolidation of the US beachheads (Utah Beach and Omaha Beach) and establishment of a continuous defensive line against expected German counterattacks. The defending German force attempted to hold the city long enough to allow reinforcements en route from the south to arrive, prevent or delay the merging of the lodgments, and keep the US First Army from launching an attack towards Lessay-Périers that would cut off the Cotentin Peninsula.

Carentan was defended by two battalions of Fallschirmjäger-Regiment 6 (6th Parachute Regiment) of the 2nd Fallschirmjäger-Division and two Ost battalions. The 17th SS Panzergrenadier Division, ordered to reinforce Carentan, was delayed by transport shortages and attacks by Allied aircraft. The attacking 101st Airborne Division landed by parachute on 6 June as part of the American airborne landings in Normandy, was ordered to seize Carentan.

In the ensuing battle, the 101st forced passage across the causeway into Carentan on 10–11 June. A lack of ammunition forced the German forces to withdraw on 12 June. The 17th SS PzG Division counter-attacked the 101st Airborne on 13 June. Initially successful, its attack was thrown back by Combat Command A (CCA) of the US 2nd Armored Division

Operation Cobra

After the amphibious assault, the Allied forces remained stalled in Normandy for some time, advancing much more slowly than expected with close-fought infantry battles in the dense hedgerows. However, with Operation Cobra, launched on 24 July with mostly American troops, the Allies succeeded in breaking the German lines and sweeping out into France with fast-moving armored divisions. This led to a major defeat for the Germans, with 400,000 soldiers trapped in the Falaise pocket, and the capture of Paris on 25 August.

Operation Lüttich

Operation Lüttich was a code name given to a German counter-attack during the Battle of Normandy, which took place around the American positions near Mortain from 7–13 August 1944. (Lüttich is the German name for the city of Liège in Belgium, where the Germans had won a victory in the early days of August 1914 during World War I.) The offensive is also referred to in American and British histories of the Battle of Normandy as the Mortain counter-offensive.

The assault was ordered by Adolf Hitler, to eliminate the gains made by the First United States Army during Operation Cobra and the subsequent weeks, and by reaching the coast in the region of Avranches at the base of the Cotentin peninsula, cut off the units of the Third United States Army which had advanced into Brittany.

The main German striking force was the XLVII Panzer Corps, with one and a half SS Panzer Divisions and two Wehrmacht Panzer Divisions. Although they made initial gains against the defending US VII Corps, they were soon halted and Allied aircraft inflicted severe losses on the attacking troops, eventually destroying nearly half of the German tanks involved in the attack. Although fighting continued around Mortain for six days, the American forces had regained the initiative within a day of the opening of the German attack.

As the German commanders on the spot had warned Hitler in vain, there was little chance of the attack succeeding, and the concentration of their armored reserves at the western end of the front in Normandy soon led to disaster, as they were outflanked to their south and the front to their east collapsed, resulting in many of the German troops in Normandy being trapped in the Falaise Pocket.

Falaise Pocket

After Operation Cobra, the American breakout from the Normandy beachhead, the Third US Army commanded by General George Patton rapidly advanced south and south-east. Despite lacking the resources to defeat the US breakthrough and simultaneous British and Canadian offensives south of Caumont and Caen