Aircraft carrier in the context of "Deterrence theory"

Air warfare was a major component in all theaters of World War II and, together with anti-aircraft warfare, consumed a large fraction of the industrial output of the major powers. Germany and Japan depended on air forces that were closely integrated with land and naval forces; the Axis powers downplayed the advantage of fleets of strategic bombers and were late in appreciating the need to defend against Allied strategic bombing. By contrast, Britain and the United States took an approach that greatly emphasized strategic bombing and (to a lesser degree) tactical control of the battlefield by air as well as adequate air defenses. Both Britain and the U.S. built substantially larger strategic forces of large, long-range bombers. Simultaneously, they built tactical air forces that could win air superiority over the battlefields, thereby giving vital assistance to ground troops. The U.S. Navy and Royal Navy also built a powerful naval-air component based on aircraft carriers, as did the Imperial Japanese Navy; these played the central role in the war at sea.

Command of the sea (also called control of the sea or sea control) is a naval military concept regarding the strength of a particular navy to a specific naval area it controls. A navy has command of the sea when it is so strong that its rivals cannot attack it directly. This dominance may apply to its surrounding waters (i.e., the littoral) or may extend far into the oceans, meaning the country has a blue-water navy. It is the naval equivalent of air supremacy.

With command of the sea, a country (or alliance) can ensure that its own military and merchant ships can move around at will, while its rivals are forced either to stay in port or to try to evade it. It also enables free use of amphibious operations that can expand ground-based strategic options. The British Royal Navy held command of the sea for most of the period between the 18th to the early 20th centuries, allowing Britain and its allies to trade and to move troops and supplies easily in wartime, while its enemies could not. In the post-World War II period, the United States Navy has had command of the sea.

The United States Navy (USN) is the maritime service branch of the United States Armed Forces and the naval warfare force of the United States. It is the world's most powerful navy with the largest displacement, at 4.5 million tons in 2021. It has the world's largest aircraft carrier fleet, with eleven in service, one undergoing trials, two new carriers under construction, and six other carriers planned as of 2024. With 336,978 personnel on active duty and 101,583 in the Ready Reserve, the U.S. Navy is the third largest of the United States military service branches in terms of personnel. It has 299 deployable combat vessels and about 4,012 operational aircraft as of 18 July 2023. The U.S. Navy is a part of the United States Department of Defense and is one of six armed forces of the United States and one of eight uniformed services of the United States.

The United States Navy traces its origins to the Continental Navy, which was established during the American Revolutionary War and was effectively disbanded as a separate entity shortly thereafter. After suffering significant loss of goods and personnel at the hands of the Barbary pirates from Algiers, the United States Congress passed the Naval Act of 1794 for the construction of six heavy frigates, the first ships of the Navy. The United States Navy played a major role in the American Civil War by blockading the Confederacy and seizing control of its rivers. It played the central role in the World War II defeat of Imperial Japan. The United States Navy emerged from World War II as the most powerful navy in the world, succeeding the British Navy. The modern United States Navy maintains a sizable global presence, deploying in strength in such areas as the Western Pacific, the Mediterranean, and the Indian Ocean. It is a blue-water navy with the ability to project force onto the littoral regions of the world, engage in forward deployments during peacetime and rapidly respond to regional crises, making it a frequent actor in American foreign and military policy.

The United States Marine Corps (USMC), also referred to as the United States Marines or simply the Marines, is the maritime land force service branch of the United States Armed Forces. It is responsible for conducting expeditionary and amphibious operations through combined arms, implementing its own infantry, artillery, aerial, and special operations forces. The U.S. Marine Corps is a part of the United States Department of Defense and is one of the six armed forces of the United States and one of the eight uniformed services of the United States.

The Marine Corps has been part of the United States Department of the Navy since 30 June 1834 with its sister service, the United States Navy. The USMC operates installations on land and aboard sea-going amphibious warfare ships around the world. Additionally, several of the Marines' tactical aviation squadrons, primarily Marine Fighter Attack squadrons, are also embedded in Navy carrier air wings and operate from the aircraft carriers.

The attack on Pearl Harbor was a surprise military strike by the Empire of Japan on the United States Pacific Fleet at its naval base at Pearl Harbor on Oahu, Hawaii, on December 7, 1941. At the time, the U.S. was a neutral country in World War II. The air raid on Pearl Harbor, which was launched from aircraft carriers, resulted in the U.S. declaring war on Japan the next day. The Japanese military leadership referred to the attack as the Hawaii Operation and Operation AI, and as Operation Z during its planning.

The attack on Pearl Harbor was preceded by months of negotiations between the U.S. and Japan over the future of the Pacific. Japanese demands included that the U.S. end its sanctions against Japan, cease aiding China in the Second Sino-Japanese War, and allow Japan to access the resources of the Dutch East Indies. Japan sent out its naval attack group on November 26, 1941, just prior to receiving the Hull note, which stated the U.S. desire that Japan withdraw from China and French Indochina. Isoroku Yamamoto, commander of the Japanese Combined Fleet, planned the attack as a pre-emptive strike on the Pacific Fleet, based at Pearl Harbor since 1940 in order to prevent it from interfering with Japan's planned actions in Southeast Asia. Yamamoto hoped that the strike would enable Japan to make quick territorial gains and negotiate peace. In addition to Pearl Harbor, over seven hours Japan launched coordinated attacks on the U.S.-held Philippines, Guam, and Wake Island; and on the British Empire in Malaya, Singapore, and Hong Kong.

Naval aviation is the application of military air power by navies, either from warships that can embark aircraft (e.g. aircraft carriers, amphibious assault ships and aircraft cruisers) or from coastal naval air stations.It often involves navalised aircraft, specifically designed for naval use.Seaborne aviation encompasses similar activities not restricted to navies, including marines and coast guards, such as in U.S. naval aviators. As with most army aviation units, naval aviation units are generally separate from a nation's dedicated air force.

Naval aviation operations are typically projected by way of carrier-based aircraft, which must be sturdy enough to withstand the demands of shipborne operations at sea. They must be able to take off from a short runway (typically the flight deck of an aircraft carrier) and be sturdy and flexible enough to come to a sudden stop when landing; they typically have robust folding or swinging wings that reduce the occupied space and thus allow more of them to be stored in below-decks hangars and limited parking spaces on flight decks. These aircraft are designed for many tactical purposes, including aerial combat, airstrike/close air support, anti-submarine warfare, early warning, search and rescue, matériel transport, weather observation, patrol and reconnaissance, and wide-area command and control duties.

A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or informally to refer to remotely operated vehicles and robots, or to medium-sized or smaller vessels (such as the midget submarine and the wet sub). Submarines are referred to as boats rather than ships regardless of their size.

Although experimental submarines had been built earlier, submarine design took off during the 19th century, and submarines were adopted by several navies. They were first used widely during World War I (1914–1918), and are now used in many navies, large and small. Their military uses include: attacking enemy surface ships (merchant and military) or other submarines; aircraft carrier protection; blockade running; nuclear deterrence; stealth operations in denied areas when gathering intelligence and doing reconnaissance; denying or influencing enemy movements; conventional land attacks (for example, launching a cruise missile); and covert insertion of frogmen or special forces. Their civilian uses include: marine science; salvage; exploration; and facility inspection and maintenance. Submarines can be modified for specialized functions such as search-and-rescue missions and undersea cable repair. They are also used in the tourism industry and in undersea archaeology. Modern deep-diving submarines derive from the bathyscaphe, which evolved from the diving bell.

The Pacific War, sometimes called the Asia–Pacific War or the Pacific Theater, was the theater of World War II fought between the Japan and the Allies in East and Southeast Asia, the Pacific and Indian Oceans, and Oceania. It was geographically the largest theater of the war, including the Pacific Ocean theater, the South West Pacific theater, the Second Sino-Japanese War, and the brief Soviet–Japanese War, and included some of the largest naval battles in history. War between Japan and the Republic of China had begun in 1937, with hostilities dating back to Japan's invasion of Manchuria in 1931, but the Pacific War is more widely accepted to have begun in 1941, when the United States and United Kingdom were brought into the war, after being attacked by Japan.

Japan invaded French Indochina in 1940, and extended its control over the entire territory in July 1941. On 7–8 December 1941, Japan attacked the American naval base at Pearl Harbor in Hawaii; the U.S.-held Philippines, Guam, and Wake Island; and the British colonies of Malaya, Singapore, and Hong Kong, followed by a Japanese declaration of war. The Japanese achieved great success over the next 6 months, allying with Thailand and capturing the listed territories (except for Hawaii) in addition to Borneo, New Britain, the Dutch East Indies, Burma, the Solomon and Gilbert Islands, and parts of New Guinea. In May 1942, Japanese and Allied aircraft carriers fought at the Battle of Coral Sea, resulting in the retreat of a Japanese invasion force headed for Port Moresby. In June, Japan invaded the Aleutian Islands, and in the central Pacific was defeated at the Battle of Midway, considered a key turning point in the war. After this point, the Japanese experienced great difficulty replacing their losses in ships and aircraft as the U.S. produced ever increasing numbers of both.