Although the U.S. had conducted amphibious operations since the Revolutionary War, it was not until after the Spanish-American War that the military services attempted to codify procedures in doctrine. Early emphasis focused on command relationships and the responsibilities of commanders, eventually expanding to incorporate operational concepts, tactical techniques, and the necessary equipment. In an environment characterized by inter-service rivalry, as well as monetary and materiel constraints, dedicated individuals and organizations overcame numerous obstacles to develop, practice, and successfully execute amphibious operations in World War II. This thesis examines the evolutionary development of amphibious doctrine by the U.S. Marine Corps, Army, and Navy, and the employment of that doctrine during Operations Watchtower and Torch in World War II. The examination includes an analysis of the historical efforts to develop innovative solutions to a wide range of challenges the services faced at the beginning of the 20th Century leading up to World War II. How the leadership solved those challenges informs the efforts of current leadership in addressing contemporary doctrinal, operational, and tactical challenges and those of the future.