Early the interwar period, Marine Major Earl Ellis envisaged the need to conquer fortified islands in the Pacific to allow the United States to conduct an amphibious assault on the territories of the Japanese nation. (USMC History Division)
“Innovate, Adapt, and Win!” is a mantra repeated in the Marine Corps Operating Concept (MOC). From tailored symposiums to the Commandant’s Innovation Challenges, the Marine Corps seems smitten by artificial intelligence, drone swarms, and manned-unmanned teaming in its attempt to stay ahead of the nation’s adversaries. While the MOC recognizes the importance of such technologies in prospective warfare and the necessity to innovate, it also states, “[m]aneuver warfare was, is, and will remain our doctrine.” MCDP-1, Warfighting , likewise insists, “equipment should be designed so that its use is consistent with established doctrine and tactics.” Doctrine provides the fundamental principles which guide military actions in support of national objectives.
The Marine Corps must develop a future-looking doctrine that provides thrust for the engines of innovation to achieve escape velocity from the gravitational pull of outmoded paradigms. If one aim is to innovate more effectively, the Marine Corps’ history and heritage provide twin tutors in how a doctrinal foundation provided the catalyst for generating post-World War I innovations that became hallmarks of the Corps.
Interwar Innovation: Doctrine First
Predicting requirements for the next major conflict based on rigid doctrine can pose problems for innovation. For instance, determining solutions too early leaves one vulnerable to potential equipment obsolescence or tied to slow acquisition processes when war arrives at an inconvenient time. Yet, if doctrine is flexible enough to support a variety of possible contingencies, it can remain relevant to the task. Early the interwar period, Marine Major Earl Ellis envisaged the need to conquer fortified islands in the Pacific to allow the United States to conduct an amphibious assault on the territories of the Japanese nation. Acting on this information from Major Ellis, Marine Corps Commandant, Major General John A. Lejeune, renewed his service’s commitment to further refining its amphibious doctrine in anticipation of needing to seize advanced naval bases in the Pacific.  Lejeune’s emphasis on developing doctrine prior to having the necessary equipment proved prophetic. By having established doctrine prior to developing solutions, the Marine Corps would ensure that when new technologies arrived its personnel had a framework for employment.
Understanding the future operating environment in the interwar period helped shape the Corps’ doctrinal underpinnings and experimentation for innovation. During this period, the Navy and Marine Corps conducted a series of the fleet landing exercises (FLEXs) that began to shape how future operations could take place based on the Tentative Manual for Landing Operations .  Before they possessed the appropriate landing craft and other necessary capabilities, these exercises informed the continuous refinement of Marine Corps doctrine that made opposed landings a viable course of action.  These exercises also demonstrated a willingness to experiment and a service culture that challenged its own doctrine to lay the foundation for future innovation. 
To innovate in the postwar period, the Marine Corps also identified gaps in doctrine that highlighted the disparities between current capabilities and future requirements. For instance, to effectively support War Plan Orange, the Marine Corps recognized it needed an amphibious capability to combat Japan, which also presented an opportunity to help distinguish itself from the Army.  This countercultural attitude, coupled with an outlook that anticipated a future island campaign, impelled the Marine Corps to pinpoint shortfalls in organic capabilities. As a result, the Marine Corps was able to link innovation to a justifiable requirement for the development of technology that supported both its doctrinal positions and anticipated future opponents.
Driven by this quest for a suitable amphibious doctrine, the Marines next envisioned an optimal capability required for such landings. Frustrated by higher headquarters’ efforts to develop an appropriate landing craft for amphibious operations, Marine officers convinced the Navy to allow competition from private industry.  By exploring different manufacturers, exchanging ideas, and building relationships with private industry, the Marine Corps was able to develop a landing craft for employment in World War II.
Doubling Down on Doctrine
The Marine Corps’s emphasis on doctrine during the interwar period influenced how Marines challenged conventional wisdom and improved the integration of forces to achieve greater combined arms effects for future operations. When the Marine Corps was threatened with elimination or absorption into other services, it reinforced its position by further developing and refining its amphibious assault doctrine. While the Army remained “skeptical” of the value of such a tactic, it conversely allowed the Marine Corps to become subject matter experts in this domain. However, the Marine Corps’s emphasis on the supremacy of doctrine did not halt at the shores of amphibious landings, but extended into the air domain as well. 
In one example regarding advances in aviation close air support, Marines stressed doctrinal improvements over new technology. By having air and ground units within the same service embrace a common doctrine, cooperation among Marine Corps units became much easier and positively contributed to their effectiveness. During this same period, the Marine Corps also published its seminal Small Wars Manual, which embodied doctrinal positions that remain relevant even in today’s War on Terror.  The prominence of doctrinal development is a thematic influence that underwrites the basis for how the Marine Corps effectively innovated in the interwar period.
Lessons learned from the Marines during the interwar period can provide an understanding for today’s militaries. While interwar periods can help a military adjust focus from previous operations towards future requirements or new adversaries, the theme of doctrine preceding innovation cannot be ignored.
MCDP-1 instructs, “[a]ny doctrine which attempts to reduce warfare to ratios of forces, weapons, and equipment neglects the impact of the human will on the conduct of war and is therefore inherently flawed.” In today’s fast-paced environment, technological innovations may only provide a momentary competitive advantage. By advancing a doctrine that understands technology’s suitable role, while maintaining a conservative outlook on war, the Marine Corps can pursue a dual strategy that appropriately places the human as the centerpiece of its warfighting capabilities.
 John P. Campbell, “Marines, Aviators, and the Battleship Mentality, 1923-33,” in Assault from the Sea: Essays on the History of Amphibious Warfare, edited by Merrill L. Bartlett (Annapolis: Naval Institute Press, 1983), 169.
 Williamson Murray and Allan R. Millett, eds., Military Innovation in the Interwar Period (Cambridge: Cambridge University Press, 1996), 72.
 Ibid , 74.
 Williamson Murray and Allan R. Millett, eds., Military Innovation in the Interwar Period (Cambridge: Cambridge University Press, 1996), 75-76.
 Murray and Millett , Military Innovation in the Interwar Period , 77.
 Robert D. Heinl, “The U.S. Marine Corps: Author of Modern Amphibious Warfare,” in Assault from the Sea: Essays on the History of Amphibious Warfare , edited by Merrill L. Bartlett (Annapolis: Naval Institute Press, 1983), 189.
 Murray and Millet, 71-72.
 Murray and Millet , 84.
 Murray and Millet, 75, 77.
 Leo J. Daugherty III, Pioneers of Amphibious Warfare, 1898-1945: Profiles of Fourteen American Military Strategists (McFarland, 2009), 171.