[adrian roberts]

The IJN had the Shokaku and Zuikako which were the only modern, purpose-built carriers they did not commit to Midway. After the loss of the four at Midway, they had to rely largely on various conversions from merchant vessels for the rest of the war [e.g. Zuiho, Junyo]. The only exceptions were Taiho and Shinano: the latter was a conversion of a Yamato/Musashi sister which gobbled up huge resources to build and made the Titanic look long-lived.
The USN had the Saratoga, Lexington's sister, which was in the Atlantic at the time. But the first of the Essex class were availble within weeks of Midway.