Historians H. P. Willmott, Jonathan Parshall, and Anthony Tully believe Yamamoto made a significant strategic error in his decision to support "MO" with strategic assets. Since Yamamoto had decided the decisive battle with the U.S. was to take place at Midway, he should not have diverted any of his important assets, especially fleet carriers, to a secondary operation like "MO". Yamamoto's decision meant Japanese naval forces were weakened just enough at both the Coral Sea and Midway battles to allow the Allies to defeat them in detail. Willmott adds, if either operation was important enough to commit fleet carriers, then all of the Japanese carriers should have been committed to each in order to ensure success. By committing crucial assets to "MO", Yamamoto made the more important Midway operation dependent on the secondary operation's success.