to Commandant John A. Lejeune, who assigned Ellis to head the Marine Corps Intelligence section of the newly established Division of Operations and Training (DOT) at Headquarters Marine Corps (HQMC). During this assignment, he prepared an essay regarding the details of military and civil operations required to eradicate subversion and insurgency, titled "Bush Brigades"'. This essay was considered controversial because Marines had been recently accused of killing local citizens in the Philippines and Haiti. As a result, "Bush Brigades" was never officially published, though it was printed and circulated among Marines and other members of the US military. For example while serving as Director of the Marine Corps Intelligence section, Ellis sent an excerpt of the essay titled "Intelligence Service in Bush Brigades and Baby Nations" to Marine Corps Intelligence units worldwide. In late 1920, Lejeune and his senior staff focused on review and revision of war plans that were prepared for use in the event of hostilities with Imperial Japan; this work included revising War Plan Orange. As part of this effort, Ellis produced the prophetic document, "Operation Plan 712 – Advanced Base Operations in Micronesia", which underscored that in the event of hostilities with Japan, the US would require advanced bases to support its fleet. The Territory of Hawaii constituted the 'only' support for the United States Navy due to the lack of naval facilities in the US possessions of the Philippines and Guam. Japan had already occupied the Marshall, Caroline, and Palau Islands, which flanked the U.S. lines of communications in the region by more than 2,300 miles. Ellis's Operation Plan 712 predicted that Japan would initiate a war, and that Japan would stay near their own territorial waters until encountered by the U.S. fleet. He also added that great losses would occur in what he termed the "ship-shore belt" because of confusion during amphibious assaults. Ellis advised war planners to minimize confusion and casualties by organizing task forces prior to leaving base ports, and to maintain unit integrity rather than dividing Marines up among several transports. ... a major fleet action would decide the war in the Pacific; the U.S. fleet would be 25 percent superior to that of the enemy; the enemy would hold his main fleet within his defense line; fleet units must be husbanded; preliminary activities of the U.S fleet must be accomplished with a minimum of assets; Marine Corps forces must be