For years, the Marine Corps has touted the prescience of Lieutenant Colonel “Pete” Ellis, USMC, who predicted in 1921 that the United States would fight Japan and how the Pacific Theater would be won. Now, for the first time, those predictions and other works by the “amphibious prophet” are available in print. Included is two works by Ellis on naval and amphibious operations, including Advanced Base Operations in Micronesia, the study of tactics and operations in the Pacific Ocean that the United States Navy and Marine Corps would use to win the war against Imperial Japan. Ellis describes the form and functions of a modern Marine Corps designed to win its Nation’s battles. Ellis’ ideas about how the Marine Corps should fight are still in use throughout the world today. Ellis’ ideas on amphibious operations are well known, but his ideas on counterinsurgency and conventional war have been overshadowed and forgotten. Ellis wrote two articles based on his warfighting experiences in the Philippines and as part of the American Expeditionary Force in Europe during World War I. These articles, last published in the early 1920’s, are both republished in this book and show Ellis as a prescient thinker who was ahead of his time. Ellis identifies concepts that the U.S. military struggles with even today, and that other thinkers would not identify for decades after Ellis’ death. Also included are six essays by the editor, introducing the ideas of Pete Ellis and putting them in a modern context. As the United States turns its focus to the Pacific, Ellis’ ideas can inform policymakers on the dynamics of strategy and warfare in the vast reaches of the Pacific Ocean. Edited by Captain B. A. Friedman, USMC, 21st Century Ellis reveals the strategic insights of Pete Ellis for then and now.