After the Pearl Harbor disaster, Kimmel was relieved by Admiral Chester W. Nimitz, who retained Kimmel's entire staff. McCormick became Nimitz' war plans officer in April 1942, serving in that capacity during the battles of the Coral Sea, Midway, and Guadalcanal. On June 30, 1942, McCormick was injured in a seaplane accident while accompanying Nimitz to Alameda Naval Air Station. Despite suffering a fractured vertebra, McCormick never went on the sick list, choosing to continue on active duty while wearing a plaster cast for three months.