In April 1941 the Imperial Japanese Navy formed the First Air Fleet, composed of all Japan's fleet and light carriers. This action created an Air Force size concentration of tactical air units in a single naval unit that was capable of overwhelming any Allied Air Force in the Pacific at that time and gaining air superiority essential for the Japanese offensive from December 1941 through April 1942.[1]

By the time of Pearl Harbor the Japanese had six heavy and four light carriers in the Pacific; three more carriers were added in 1942.  By comparison U.S. Navy had just three heavy carriers available in the Pacific at the time of Pearl Harbor, providentially they were all spared Admiral Yamamoto’s intended knock out blow on December 7.  The six heavy carriers used in the Pearl Harbor Raid represented the greatest concentration of naval air power achieved up to that time. 

The U.S. Navy moved three Atlantic Fleet heavy carriers to the Pacific in 1942.  During that year the six American carriers and their air groups fought four major naval battles with their Japanese counterparts.  By late 1942 only one U.S. heavy carrier and two Japanese heavy carriers were left fully operational.  At that point neither carrier force was strong enough to dominate the Pacific’s land based air forces which were growing both in size and tactical skill.

One of the causes of the war was the United States’ Two Ocean Navy building program.  In 1940 the U.S. essentially committed itself to building a navy that was big enough to take on all the other navies of the world combined.  Included in this naval construction program were 10 heavy carriers.  The success of the Japanese carriers at the beginning of the war ensured that aircraft carrier construction received very high priority.  As a result nine light cruisers, then under construction, were converted to fast light carriers and commissioned in 1943.  By November 1943, almost two years after the start of the war, the U.S. Navy took the offensive in the Central Pacific with a Fast Carrier Task Force consisting of four of the new heavy carriers and five of the new light carriers plus the two remaining pre war heavy carriers.  For the rest of the war a new heavy carrier was commissioned about every 60 days. Like the Japanese First Air Fleet before it, this force, later known alternately as Task Force 38 or Task Force 58, could defeat any Japanese air force it encountered in the Western Pacific.  The fast carrier force fought two major battles in 1944 and provided air cover for most of the major amphibious assaults undertaken from November 1943 through the end of the war.

Each fast carrier was assigned an air group of two to four squadrons.  Heavy carriers accommodated approximately 100 aircraft while light carriers accommodated approximately 33.  After the navy’s TBD squadrons were decimated at Midway the TBF/TBM Avenger became the standard torpedo bomber on U.S. carriers.  A heavy carrier air group had between 12-18 Avengers and a light carrier air group had 9 Avengers. 

The SBD was the standard dive bomber for the first half of the war and was replaced by the SB2C in 1944.  In 1943 a heavy group had 36 SBD and a light carrier group had 9 SBD.  As fighters became more capable and the kamikaze threat emerged fighters were substituted for dive bombers so that by the end of the war the standard bomber complement of a heavy group was 15 SB2C and 15 TBM.  

The F4F was the standard carrier fighter in 1942.  It was replaced by the F6F in 1943 which in turn was supplemented by the F4U in 1945.  The number of fighters on heavy carriers grew from 18 at the beginning of 1942 to 73 in 1945.  The fighter complement on light carriers grew from 12 in 1943 to 24 in 1945.  For Olympic, heavy carrier fighter complements were to be reduced to 56 and light carrier groups would contain only fighters.  The planned light carrier complement initially was three dozen F6Fs or F4Us with the ultimate goal of four dozen of the smaller F8Fs.  F8F equipped air groups were in the pipeline to the Western Pacific as the war ended.

Initially carrier air groups were assigned permanently to carriers and squadrons were rotated through the groups as circumstances warranted.   At time progressed the navy found it more effective to manage groups than squadrons and groups were assigned to carriers for specific tours of duty.  As the war progressed the intensity of operations increased the tour lengths were shortened.  For all of 1944 and 1945 aircraft attrition on the active carriers was more than 20% per month.

By May 1945 nine heavy carrier air groups were in action and thirty five additional heavy carrier groups were at various stages of training.  This total was approximately two air groups for each heavy carrier that was in commission or was planned to be commissioned by the end of the training cycle.[2]