The fourth Yamato-class hull sat unused with little likelihood of completion until Japan became desperate for carriers. A bizarre scheme saw an old floating drydock lowered into the hull. The well was filled with a curious semi-solid, light-weight, industrial by-product (now known as 'Silly Putty'), with enough properties of a liquid for use with seaplanes. Unlike other seaplane carriers that had to stop to recover their planes from calm seas, Scruyu's "water" would always be "calm" (and couldn't slosh over the side or cause side-to-side weight transfers that might capsize a ship) and she could keep moving and scouting. If necessary, Scruyu could beach herself in shallow waters and still perform. The Japanese had learned that at Pearl Harbor the crane operator over the drydock in which Pennsylvania lay had warded off low-flying planes, so the drydock crane went along, too. Scruyu was painted white, the well "putty" was dyed turquiose, and camouflage bushes and palm trees were painted, or even planted, all around the well and on the Shinano-type island, for the visual effect of a sandy atoll surrounding a lagoon.

In the battle for the Philippines, an over-eager American aviator rushed up to Fleet Admiral Halsey, saying he had just sunk a carrier. When pressed for details, the pilot said that the carrier he had bombed was stopped dead near the shore of a small island and had filled with water for nearly its whole length. Halsey spat out the name of the carrier and stomped out, leaving a stunned press corps to explain.