A Japanese force was sent north to attack the Aleutian Islands. The next stage of the plan called for the capture of Midway, which would give him an opportunity to destroy Nimitz's remaining carriers. In May, Allied codebreakers discovered his intentions. Nagumo was again in tactical command but was focused on the invasion of Midway; Yamamoto's complex plan had no provision for intervention by Nimitz before the Japanese expected him. Planned surveillance of the U.S. fleet by long range seaplane did not happen (as a result of an abortive identical operation in March), so Fletcher's carriers were able to proceed to a flanking position without being detected. Nagumo had 272 planes operating from his four carriers, the U.S. 348 (115 land-based).