In 1939 the US Navy had 15 battleships, 5 aircraft carriers, 18 heavy cruisers and 19 light cruisers. Since the 1920s the US Navy was based on the view that the Japanese Navy posed the main threat to the United States. As a result, the US Navy was the only country capable of rivaling Japan in the field of naval aviation. The Lexington and Saratoga aircraft carriers had appeared in 1927. The navy also retained control over specialist carrier aircraft such as the Grumman Hellcat and Douglas SBD-3.
After the outbreak of the Second World War the US government became concerned about the dangers posed by Japan. Congress passed the Two Oceans Navy Bill in July 1940 allowed for the building of 1,325,000 tons of new warships. The following year eight battleships and three aircraft carriers were added to the strength of the US Navy.
In January 1941, the Commander in Chief of the Japanese Combined Fleet, Admiral Isoruku Yamamoto began planning for a surprise attack on the US Navy at Pearl Harbor. Yamamoto feared that he did not have the resources to win a long war against the United States. He therefore advocated a surprise attack that would destroy the US Fleet in one crushing blow.
Yamamoto's plan was eventually agreed by the Japanese Imperial Staff in the autumn and the strike force under the command of Vice Admiral Chuichi Nagumo sailed from the Kurile Islands on 26th November, 1941.
Richard Sorge, a German journalist working as a Soviet agent in Tokyo, discovered details of the plan for the attack on Pearl Harbor. However, this information does not seem to have been passed onto the United States. US Army intelligence. It did intercept two cipher messages from Tokyo to Kichisaburo Normura, the Japanese Ambassador to the United States, that suggested an imminent attack, but Richmond Turner, in charge of evaluating and dissemination, did not pass on warnings of the proposed attack to Admiral Husband Kimmel.
Nagumo's fleet was positioned 275 miles north of Oahu. On Sunday, 7th December, 1941, 105 high-level bombers, 135 dive-bombers and 81 fighter aircraft attacked the the US Fleet at Pearl Harbor. In their first attack the Japanese sunk the Arizona, Oklahoma, West Virginia and California. The second attack, launched 45 minutes later, hampered by smoke, created less damage.
In two hours 18 warships, 188 aircraft and 2,403 servicemen were lost in the attack. Luckily, the navy's three aircraft carriers, Enterprise, Lexington and Saratoga, were all at sea at the time. The following day, President Franklin D. Roosevelt and a united US Congress declared war on Japan.
After Pearl Harbor the US Navy had 16 battleships, 7 aircraft carriers, 18 heavy cruisers, 19 light cruisers, 6 anti-aircraft cruisers, 171 destroyers and 114 submarines. As well as the war in the Pacific the US naval forces helped the Royal Navy to maintain ocean supply lines to Britain in the Atlantic.
Ten days after the attack Admiral Chester Nimitz removed Admiral Husband Kimmel from office. The subsequent investigations into the attack found Kimmel guilty of errors of judgement and not coordinating army-navy efforts to defend Hawaii. In May 1942, Kimmel decided to take early retirement.
After entering the Second World War passed an emergency war building programme. Sixteen large aircraft carriers such as the Essex were ordered. So also were fifteen new battleships and nine smaller Independence class aircraft carriers. Destroyers, escort carriers and other anti-submarine vessels were built to meet the twin threat of U-Boats in the Atlantic and Japanese submarines in the Pacific.
New naval aircraft such as the the Grumman Hellcat, the Chance-Vought Corsair were also ordered. Over the next four years over 50,000 combat aircraft were delivered to the US Navy. In the same period aviation personnel rose from 10,923 to 437,524.
In March 1942, Admiral Ernest King became Commander-in-Chief of the US Navy. Under King's leadership the fleet grew rapidly and within three years surpassed the combined strength of all other navies in the conflict. This included 5,788 warships and 66,000 landing craft.
Admiral Ernest King, Admiral Chester Nimitz, Commander in Chief of the US Pacific Fleet, and General Douglas MacArthur, Supreme Commander of the Southwest Pacific, decided that their first objective should be to establish and protect a line of communications across the South Pacific to Australia. This resulted in the battle of Coral Sea (6th-8th May, 1942).
In 1942 Admiral Isoruku Yamamoto decided to try and capture the US base on Midway Island. He believed that the Japanese Air Force would be able to launch air attacks on the US Fleet at Pearl Harbor. Yamamoto devised a complex plan where the Combined Fleet was split into eight task groups. Two of these groups made a diversionary attack on the Aleutian Islands. The rest of the fleet led by Yamamoto, Vice Admiral Chuichi Nagumo and Vice Admiral Nobutake Kondo, would head for Midway.
Unknown to Yamamoto the US intelligence service and broken the Japanese communication code and informed Admiral Chester Nimitz of the Japanese plans. Nimitz was able to assemble two task forces under Admiral Frank Fletcher and Rear Admiral Raymond Spruance. With the carriers Yorktown, Enterprise and Hornet, eight cruisers, and fifteen destroyers, they also headed for Midway.
On 3rd June, 1942, 100 aircraft from Nagumo's carrier force bombed Midway. The US Marine fighters were outnumbered and were unable to stop extensive damage being caused. While the Japanese aircraft were being rearmed they were attacked by carrier planes from Spruance's Task Force.
While this was taking place Yorktown and Enterprise arrived and scored hits on the Japanese ships, Akagi, Soryu and Kaga. The Hirpu managed to sink the Yorktown before it was set afire by the Enterprise. The Japanese Navy had now lost all four of her aircraft carriers and Admiral Isoruku Yamamoto was forced to order a withdrawal.
Admiral William Halsey took control of naval operations during the Guadalcana campaign (12th-13th November, 1942) and sunk two Japanese battleships, two destroyers and six transport ships for the loss of two cruisers and four destroyers.
General Douglas MacArthur also 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.
The US Marines, the US Navy's land army, played an important role in these operations and were reorganized as the Marine Amphibious Corps. Under the leadership of General Holland Smith, the Marine Corps employed a force of over 450,000 men and was primarily employed as the spearhead of the amphibious operation in the Pacific.
In October, 1942, TG 16 (Enterprise) and TG 17 (Hornet) were combined to form TG 61 and was placed under the command of Rear Admiral Thomas Kinkaid. He faced Nobutake Kondo at the battles that took place at Santa Cruz Islands (26th-27th October, 1942). During the battle Hornet was sunk and the Enterprise was severely damaged. However, the Japanese Navy had greater difficulty replacing her losses and found it difficult to provide supplies to the Japanese Army in the region.
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 losing four carriers, three battleships and ten cruisers. Japan also had 48,000 men killed on Leyte.
In the Leyte Gulf campaign Admiral William Halsey had the task of supporting the landing of troops and to destroy the main Japanese fleet. On 24th October 1944 Halsey fell into a Japanese trap when he headed north with all 64 ships to attack Admiral Jisaburo Ozawa . He left the San Bernardino Strait unprotected and only the actions of Vice-Admiral Thomas Kinkaid and the 7th Fleet prevented a military disaster.
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 this amphibious 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 United States 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.
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. This made it comparable to the Normandy landing in mainland Europe in June, 1944.
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.
Between July 1940 and September 1945, personnel strength grew from 203,127 to 4,064,455. This figure included the US Marine Corps and the US Coastguard.