While ardently constructing impressive super-battleships, Japan reluctantly realized that heavily armored carriers were a better use of shipbuilding material. In a deal with powerful Navy "battleship admirals", a Shokaku-class CV under construction was made into battlecruiser Aratama and material was consolidated and set aside for battleship Yokozuna. In turn the proposed battleships Musashi and Shinano could be remodeled into Japan's largest aircraft carriers.

The Navy ordered the two partially-constructed battleships converted to CV's while on the slipways. Originally they were not intended to have an air complement of their own, but their shops and stores would replenish planes from other, more vulnerable carriers, and their armored decks would provide more landing spaces for displaced aircraft and some shelter from bombs (Oh, what these carriers could have done for the IJN at Midway!). A small complement of the latest "Grace" attack bombers and "Sam" fighters was added later to give a small offensive punch. Their pilots were some of the last of the highly-trained aircrews before the "Emergency Pilot Program" lowered the standards, and they were eager to be assigned to the newest and largest CV's in the Imperial Navy.

Musashi and Shinano formed Car.Div. 6 and first served the Fleet during the Marianas campaign. Though designed to stay in the rear of the fleet as support ships, the heavily armored pair were put in the van to absorb the initial attacks so that the less-protected carriers had a better chance of surviving. Car. Div. 6's aircraft found and sank the American angled-deck carrier Bon Homme Richard but both Japanese giants succumbed to massive air attacks, requiring over thirty torpedoes and 45 bombs to sink.