On 19 February 1945, U.S. Marines of the Fifth Amphibious Corps waded through the sand and surf of the Japanese-held island of Iwo Jima. As the determined Marines fought their way across the battlefield, American Joint Assault Signal Companies (JASCOs) coordinated air, sea, and land firepower to aid the Marines in their formidable task. Marine Corps historians Jeter Isely and Philip Crowl later acknowledged the key role played by JASCOs when they proclaimed that "coordination among the three supporting arms was superb throughout the operation." This thesis explores the evolution of supporting arms coordination in the Pacific War and the manifestation of that evolution, the Joint Assault Signal Company. Nonexistent at the outbreak of the Pacific War, the JASCOs that directed such overwhelming firepower at Iwo Jima were the result of nearly two years of wartime adaptation. Based on lessons learned in the war's early campaigns, the Marines acknowledged--among other concerns--a need for improved coordination of supporting fires. Created in direct response to these early combat lessons, Joint Assault Signal Companies were an example of war-induced military adaptation in doctrine, training, organization, and operational tactics. By studying this process of innovation and adaptation during war, the project reveals how a small, specialized service applied lessons learned in combat to produce a hybrid solution that spanned the wartime realms of organization, training, and tactics. So often in war, victory belongs to the unit that can successfully adjust to its environment and enemy before the opponent. In their crucial role coordinating American amphibious combat power during the Second World War, the Joint Assault Signal Companies did just that.
