 En route to Japan, the Fifth Carrier Division was diverted to Truk to support Operation Mo (the planned capture of Port Moresby in New Guinea). While they were preparing for the mission, the Americans intercepted and decrypted Japanese naval messages discussing the operation and dispatched the carriers Yorktown and Lexington to stop the invasion. The Japanese opened Operation Mo by occupying Tulagi, in the Solomon Islands, on 3 May. American land-based aircraft had spotted the light carrier Shōhō escorting the transports of the main invasion force on 6 May, and the American carriers moved west to place themselves in a position to attack it the following morning.
