Before the outbreak of the Second World War the US Army was a small professional force of 175,000 men. After the German Army invaded Poland in September 1939, General George Marshall, the new Chief of Staff, embarked on an attempt to rapidly improve the ability of the army to wage war. This included the decision to order modern tanks such as the Grant M3.
In 1940 the United States introduced selective conscription and by the following year the US Army had grown to 1,400,000 men. The Japanese attack on Pearl Harbor resulted in a further expansion of the American armed forces. Over the next three years 100 divisions were raised. Of these, 76 were infantry, 16 armoured, 5 airbourne and 2 cavalry.
The US Army's first major combat experience was against General Erwin Rommel in Tunisia. However, most action during the war was in the South-West Pacific area under the command of General Douglas MacArthur. In the summer of 1942 fighting in the Pacific was concentrated around Rabaul, the key Japanese military and air base in the Soloman Islands. On 7th August there were landings at Guadalcanal. Over the next eight months there were ten major land battles and seven major naval engagements in this area.
In 1944 General Dwight Eisenhower was put in charge of what became known as Operation Overlord, the planned landing of Allied troops in France. Eisenhower had the task of organizing around a million combat troops and two million men involved in providing support services.
The plan, drawn up by George Marshall, Dwight Eisenhower, Bernard Montgomery, Omar Bradley, Bertram Ramsay, Walter Bedell-Smith, Arthur Tedder and Trafford Leigh-Mallory, involved assaults on five beaches west of the Orne River near Caen (codenamed Sword, Juno, Gold, Omaha and Utah) by the British 2nd Army and the American 1st Army. Follow-up forces included the Canadian 1st Army and the American 3rd Army under Lt. General George Patton.
On 6th June, 1944, 2,727 ships sailed to the Normandy coast and on the first day landed 156,000 men on a front of thirty miles. It was the largest and most powerful armada that has ever sailed.
The Allies also sent in three airborne divisions, two American and one British, to prepare for the main assault by taking certain strategic points and by disrupting German communications. Of the 23,000 airborne troops, 15,500 were Americans and of these, 6,000 were killed or seriously wounded. Over the next couple of days 156,215 troops were landed from sea and air in Normandy, at a cost of some 10,300 casualties.
In 1944 General Douglas MacArthur, Supreme Commander of the Southwest Pacific, developed what became known as his island hopping tactics. This strategy involved amphibious landings on vulnerable islands, therefore bypassing Japanese troop concentrations on fortified islands. This had the advantage of avoiding frontal assaults and thus reducing the number of American casualties.
On 20th October, 1944, General Walter Krueger and the US 6th Army landed on Leyte. This was followed by Leyte Gulf, the largest naval engagement in history. It was a decisive victory for the Allies with the Japanese Navy lost four carriers, three battleships and ten cruisers. Japan also had 48,000 men killed on Leyte.
US forces returned to the Philippines when they landed on Luzon on 15th December, 1944. On the beach MacArthur announced: "People of the Philippines: I have returned. Rally to me." The Japanese Army, under General Tomoyuki Yamashita, fought a vigorous rearguard action and progress was steady but slow during 1945.
It was now decided to try and capture the small volcanic island of Iwo Jima that was defended by 20,000 veterans of the Japanese Special Naval Landing Force. During February, 1945, the Japanese, who had created a fortress on Mount Suribachi, faced an immense air and sea bombardment launched by the 5th Fleet under Admiral Raymond Spruance.
On 19th February, American soldiers began landing on the island. Over 250,000 men and 900 ships were involved in thisamphibious operation. The main objective was to capture the island's three airstrips and to to obtain a forward air base for the planned Allied attack on the Japanese home territories.
The US Army managed to capture Mount Suribachi in three days but strong resistance from the Japanese meant that the second airstrip at Motoyama was not won until 28th February, 1945. The final stage of the fighting took place in the fortified hills and these last defensive positions were not taken until 10th March.
Small groups of Japanese soldiers carried on fighting and the three airfields were not ready to receive the vast fleets of B-29 Superfortress bombers until the end of March. Of the 23,000 Japanese soldiers defending Iwo Jima, only 216 were taken alive. The American forces also suffered during the bitter fighting on the island with 5,391 Marines killed and 17,400 wounded.
The United States Army Air Force was now able to use the island to launch bombing attacks on Japan. The large number of Japanese buildings made of wood made it easy for the bombers to create firestorms. On the 9th and 10th March 1945, a raid on Tokyo devastated the city. This was followed by attacks on Nagoya, Kobe, Oska and Yokohama. An estimated 260,000 were killed and 9.2 million left homeless.
MacArthur's last amphibious operation was at Okinawa. Lying just 563km (350 miles) from the Japanese mainland, it offered excellent harbour, airfield and troop-staging facilities. It was a perfect base from which to launch a major assault on Japan, consequently it was well-defended, with 120,000 troops under General Mitsuru Ushijima. The Japanese also committed some 10,000 aircraft to defending the island.
After a four day bombardment the 1,300 ship invasion forced moved into position off the west coast of Okinawa on 1st April 1945. The landing force, under the leadership of Lieutenant-General Simon Buckner, initially totalled 155,000. However, by the time the battle finished, more than 300,000 soldiers were involved in the fighting.
On the first day 60,000 troops were put ashore against little opposition at Haguushi. The following day two airfields were captured by the Americans. However when the soldiers reached Shuri they came under heavy fire and suffered heavy casualties.
Reinforced by the 3rd Amphibious Corps and the 6th Marine Division the Americans were able to repel a ferocious counter-attack by General Mitsuru Ushijima on 4th May. At sea off Okinawa a 700 plane kamikaze raid on 6th April sunk and damaged 13 US destroyers. The giant battleship, Yamato, lacking sufficient fuel for a return journey, was also sent out on a suicide mission and was sunk on 7th May.
On 11th May, Lieutenant-General Simon Buckner, ordered another offensive on the Shuri defences, and the Japanese were finally forced to withdraw. Buckner was killed on 18th June and three days later his replacement, General Roy Geiger, announced that the island had finally been taken. When it was clear that he had been defeated, Mitsuru Ushijima committed ritual suicide (hari-kiri).
The capture of Okinawa cost the Americans 49,000 in casualties of whom 12,520 died. More than 110,000 Japanese were killed on the island.
While the island was being prepared for the invasion of Japan, a B-29 Superfortress bomber dropped an atom bomb on Hiroshima on 6th August 1945. Japan did not surrender immediately and a second bomb was dropped on Nagasaki three days later. On 10th August the Japanese surrendered and the war was over.
The US Army employed 10,420,000 men and women during the Second World War. Overall casualties were 234,874 dead, 701,385 wounded and 124,079 imprisoned.