War Plan Orange
In addition to his work on the coastal defense problem, McNair was also responsible for directing a review of War Plan Orange, the Army and Navy joint defense plan for countering an attack on Hawaii by Japan. This possibility was a major concern of U.S. military leaders during the years between World War I and World War II. Among McNair's contributions to updating this plan was the creation of several contingency plans ("branches and sequels" in Army parlance) to augment the main war plan. These contingency plans included: using chemical weapons to defend against a Japanese attack, declaring martial law in Hawaii, and determining how to maintain a defense against Japanese invaders while waiting for reinforcements from the U.S. mainland.