Aircraft carrier operations during World War II

It became apparent early in the war that control of the air was prerequisite for successful surface action both on land and at sea.[lower-alpha 2][9] For much of the war, Britain and America fought mainly on the seas,[10] where successful Allied naval operations permitted effective support and reinforcement of troops in North Africa, the Soviet Union, Western Europe and the Pacific. These operations also crippled similar efforts by Italy and Japan to sustain the empires they built by conquest. By 1942, aircraft carriers with the striking power provided by hundreds of warplanes delivering bombs and torpedoes to targets hundreds of miles away[11] supplanted battleships with big guns as the principal warships around which navies assembled task forces for major campaigns.[12]

Only America, Britain, and Japan made significant use of aircraft carriers during World War II.[lower-alpha 3] The following table shows the number of each type of carrier the principal combatants operated that had flight decks capable of both launching and recovering aircraft at sea and that were operational sometime between July 1937 and August 1945. The counts include carriers in service before the war began as well as those commissioned during the war.

Details and sources are provided at Lists of aircraft carriers operational during World War II.

World War II fleet carriers typically displaced 20,000 to 35,000 tons and could sail at 30 to 35 knots. Japanese and American fleet carriers were typically capable of carrying 50 to 90 aircraft into combat. British carriers were designed with armored decks, a measure that provided significantly greater protection against bombs and kamikazes. The additional weight of the armor, however, reduced their typical carrying capability to 35 to 55 aircraft. Thus their additional defensive measures limited their offensive striking power until Britain introduced a new carrier class late in the war.

Light aircraft carriers were fast enough to keep up with the fleet carriers but their smaller size typically reduced their aircraft load to between 30 and 50. The design of those commissioned immediately after the war began typically reflected the immediate need for fast carriers and took advantage either of having other ship hulls available for conversion to aircraft carriers or the available capacity of commercial shipyards to build them. While these carriers made contributions to the war efforts, their relatively small size made them operationally inefficient. The measure of navel power in the Pacific Theater was the number of fleet carriers a navy had.[13]

Escort carriers were smaller, slower, lightly armored, and carried 20 to 30 aircraft. They were not typically included with naval battle fleets, but before the war was over, escort carriers had performed every function that the larger carriers did.

Merchant aircraft carriers (MACs) transported grain and oil in the holds below the flight deck and carried 3 or 4 aircraft to protect themselves and other ships in convoys in which they traveled. None were used for offensive operations.

Land-based aircraft as well as carrier-launched aircraft fought at sea. In the Atlantic Theater, German and Italian aircraft attacked Allied convoys that were protected by fighter aircraft from Allied airfields as long as convoys were within fighter range. As carriers became available, Allied carrier-launched fighters provided protection in those ocean areas that could not be protected by land-based planes. In the Pacific Theater, Japan's successful expansion was typically achieved by progressively using land-based aircraft to support invasions of new areas that were within striking distance of airbases that they had established on previously conquered areas. For the Allies, land-based aircraft at local airfields contributed significantly to America's defense of Midway Island and Guadalcanal.[14] Naval fighters and bombers that operated from land-based airfields were typically delivered to battle zones by aircraft carriers. In both theaters, carrier-launched aircraft played significant roles in dominating the air, and construction of aircraft carriers received priority.

At the same time that America, Britain, and Japan began emphasizing aircraft carrier construction, they de-emphasized construction of battleships. Before the war, the number of battleships a country operated was universally regarded as the principal indicator of naval power.[15] Japan's raid on Pearl Harbor sank or damaged eight[lower-alpha 10] of America's eighteen[lower-alpha 11] battleships. America repaired and returned six of those eight battleships to service[lower-alpha 12] but commissioned only eight new battleships during the rest of the war.[lower-alpha 13] During the period September 1939 to August 1945, America commissioned ten new battleships while Japan commissioned only two and converted two existing ones to hybrid aircraft carriers. Britain commissioned five new battleships. Germany, Italy, and France together commissioned a total of six. All together, only 23 new battleships were added to combatants' fleets during the war years[lower-alpha 14] compared to 55 new fleet and light carriers.

During the entire war, battleship guns sank only a single fleet carrier and a single battleship.[lower-alpha 15] In comparison, carrier-launched aircraft damaged, sank, or took part in sinking 19 battleships.[lower-alpha 16] Although Japan was first to recognize and exploit the greater effective striking power of aircraft carriers over battleships, she was slow to abandon employment of the latter. She commissioned battleships in 1941 and 1942 that were the largest and most heavily armed ever built.[lower-alpha 17] After the losses at the Battle of Midway, however, Japan changed naval tactics and began leaving battleships out of major naval engagements.[16] America began primary reliance upon its aircraft carriers for offensive operations early in the Pacific war out of necessity after the destruction of its Pacific battleship fleet during the Japanese raid on Pearl Harbor.

Aircraft carriers were used for a wide variety of combat and combat support functions during the war. These included:

• Naval battles, during which carrier aircraft attacked each other and enemy warships, as they did during the Battle of Midway between American and Japanese fleets.
• Invasions, during which carrier aircraft provided support for amphibious landings and for occupying enemy-held positions by bombing those positions before, during, and after landings; spotting for warship guns, sometimes even controlling the firing;[17] delivering replacement aircraft and aircrews to other carriers and to airfields after successful landings, as during the American invasion of Iwo Jima.
• Raids, during which carrier aircraft attacked enemy positions to degrade them but without the intention of landing and occupying those positions, as during the Japanese raid on Ceylon.
• Anti-shipping missions, during which carrier aircraft blockaded enemy ports or attacked enemy shipping and shipping facilities, as during the Allied attacks around Bodø, Norway.
• Anti-raider missions, in which carrier aircraft searched for and attacked enemy surface ships engaged in raiding enemy merchant shipping, as during the British sinking of the Bismark.
• Anti-submarine missions, during which submarine hunter-killer groups operating independently from convoys searched for and destroyed enemy submarines, as was accomplished by groups centered on USS Bogue during the Battle of the Atlantic.
• Convoy Escort, during which carrier aircraft searched for and attacked enemy aircraft and submarines that threatened a convoy's merchant ships, as when HMS Audacity accompanied Convoy HG 76 to Britain from Gibraltar.
• Transport, during which carriers delivered aircraft and aircrews to land bases or other carriers, as USS Long Island (CVE) did for Henderson Field on Guadalcanal and as the "CVE Plane Transport Unit" did during the invasion of Okinawa.[lower-alpha 18]
• Training, during which carriers were dedicated to training pilots and/or conducting operating trials to improve carrier tactics and procedures. IJN Hōshō, HMS Furious, and USS Ranger spent long periods dedicated to training during the war.
• Repatriation, during which carriers, after the war, participated in returning military personnel to their home countries, as was done under America's Operation Magic Carpet.

Historian Craig Symonds lists three key factors enabling the Allies to win the war: British "grit", Russian manpower, and American industrial strength.[18] Specifically, Britain continued alone in Europe against all odds for a year after the fall of France, stubbornly and successfully resisting the Axis. Thirty-five million Soviet Union soldiers fought during the war, as many as the United States, Germany, and Japan combined. She lost an estimated ten million soldiers to combat deaths, many more than any other combatant. America produced more artillery pieces, tanks, ships, and aircraft than all Axis countries combined,[19][lower-alpha 19] including over 70% of the aircraft carriers commissioned during the war.

Details and sources are provided at Lists of aircraft carriers operational during World War II

Historian Richard Overy points out that statistics demonstrating material superiority are not by themselves sufficient for explaining why the Allies won the war.[20] Less easily quantifiable factors also played a significant part. The political will to fight and willingness of individual combatants to sacrifice was present within both the Allies and Axis. However, the timing of mobilizing manufacturing, technological, and manpower responses was also very important. America and Russia mobilized men and industrial capacity to rebound from significant military setbacks more quickly than anticipated by the attacking Axis powers. Important technological advances achieved by the Allies during the war outpaced those of the Axis powers in both offensive and defensive weapons systems. The Allies had greater and more strategically significant successes with code-breaking. The Allies placed greater emphasis than Axis powers on logistical support for men fighting on the front, enabling them to fight more efficiently and effectively. Geographical configurations, namely the English Channel, Atlantic Ocean, and Pacific Ocean, helped isolate British and American home bases from attack.[21][22] Significant strategic offensive decisions by Axis leaders proved unsound, creating opportunities that the Allies.[lower-alpha 20] Finally, luck played an important part in some decisive battles.[23][24] Many of these factors played important parts in enabling the Allies to dominate the seas, a central reason, according to historian Evan Mawdsley, for their emerging victorious in the war.[22] Nonetheless, while statistics relating to industrial capacity to produce arms and planes and ships do not tell the whole story, they remain an important part of it.

Successful Allied initiatives at El Alamein, Stalingrad, French North Africa, and Guadalcanal in November 1942 marked strategic shifts for World War II. Aircraft carriers contributed to the success of these operations by protecting convoys of armaments and other supplies to Egypt and Russia, keeping Malta supplied and able to disrupt Axis supply operations to North Africa, providing air support for troops during the invasion of North Africa, and by helping prevent Japanese troops and supplies from reaching Guadalcanal. Beginning in 1943, the extensive mobilization of American production capability for war resulted in dramatic increases in the number of carriers available for even more strategic initiatives. Overall, aircraft carriers contributed greatly to making 1942 the pivotal,turning point of the war, 1944 the decisive year, and 1945 one for essentially finishing up, albeit at great cost.[25][26]

In the Atlantic Theater, successful transportation of troops, aircraft, tanks, oil, and food from or routed through North America or up the West African coast to Britain, Russia, North Africa, and continental Europe was essential for ultimate Allied victory. Allied aircraft carriers screened by corvettes, destroyers and destroyer escorts proved more successful and cost-effective than battleships or cruisers for protecting convoys from attacks by Axis submarines, raiders, and land-based aircraft. By mid-1943, the Axis threat of cutting essential Allied supply lines had passed. By this time, however, German battleships and submarines had sunk six British carriers[lower-alpha 21]

In the Pacific Theater, a force of six Japanese fleet carriers with their combined aircraft striking power, the Kidō Butai, acted as a unit and roamed virtually at will for the first six months of the war. It made destructive raids against enemy positions from Hawaii in the east to India in the west and effectively supported Japanese invasions of the American Philippines, British Malaya and Burma, and the Dutch East Indies. Between May and October 1942, however, Japan and America fought four major battles between fleets centered around their aircraft carriers. During these battles, opposing warships never came within sight of each other nor fired their guns at other warships. Aircraft alone did the attacking. The first of these battles thwarted the Japanese attempt in the Coral Sea to isolate Australia. The second halted the expansion of Japanese control eastward in the Pacific toward Midway Island. The next two helped sustain the American presence on Guadalcanal. These four engagements[lower-alpha 22] were costly for both sides. At the time Pearl Harbor was attacked, Japan had a total of nine fleet and light carriers in the Pacific Theater. America had four in the Pacific with another two far away in the Atlantic. At the end of October 1942, after battle attrition from sinkings and damages, Japan had only three such carriers operational in the Pacific Theater and America, for a two-week period, had none. Though costly,the battles were strategically advantageous for the Americans, contributing significantly to the shift of strategic initiative in the Pacific Theater from Japan to America.

America was better able make good on their losses from these battles. From October 1942 until the end of the Pacific war, America commissioned 26 new fleet and light carriers. Japan commissioned eight. Over the entire war, the Allies commissioned a total of 181 carriers of all types compared to Japan's total of 19.

Details and sources are provided at Lists of aircraft carriers operational during World War II

The number of aircraft carriers operational for combat missions at any time was typically less than the total number of carriers afloat. For example, at the end of October 1942 following the Battle of the Santa Cruz Islands, only seven (47%) of the fifteen fleet and light carriers the combatants had afloat worldwide were operational. Japan had six such carriers afloat but only three were operational.[lower-alpha 29] America had three afloat, but one was in the Atlantic and the other two were damaged, leaving no operational carriers in the Pacific.[lower-alpha 30] Britain had six afloat, all in the Atlantic, but only three were operational.[lower-alpha 31] In short, although the Allies at that time had nine carriers afloat worldwide to oppose the six the Axis powers (Japan) had afloat, the combat operational reality in the Pacific was that, for a short period, there were zero Allied carriers that were operational to oppose Japan's three operational carriers.

As the war progressed, the relative number of operational carriers available for combat by each side depended upon 1)construction rates for new carriers, 2)losses due to sinkings, 3)how quickly carriers damaged in combat could be brought back into service, and 4)the time required for routine overhauls, refits for carriers to perform specific functions, and upgrades for older carriers. Short-term naval capabilities, plans, and outcomes were determined by the number of carriers that were operational during any given month. The impact of the relative number of operational, combat-ready carriers available was particularly felt during 1942, when the strategic initiative in the Pacific Theater passed from Japan to America.

Details may be found at Atlantic Theater aircraft carrier operations during World War II.

Details may be found at Pacific Theater aircraft carrier operations during World War II.

Details regarding carrier aircraft may be found at Carrier aircraft used during World War II.

Lists of aircraft carriers by carrier type for each country may be found at Lists of aircraft carriers operational during World War II.

Names, dates, and participating aircraft carriers for each military operation may be found listed chronologically at Lists of aircraft carrier operations during World War II.

Information about design and capability of carriers may be found at Design and capability of aircraft carriers during World War II.