Another excerpt from John Sayen’s Battalion: An Organizational Study of United States Infantry (unpublished, but serialized on Bruce Gudmundsson’s Tactical Notebook:
The 1919 demobilization was nearly as traumatic for the Marines as it was for the Army. Their numbers fell from a peak of 75,000 to about 1,000 officers and 16,000 enlisted in 1920. Authorized strength was 17,400. The 15 Marine regiments and at least three, probably four, machinegun battalions existing at the end of November 1918 had withered away to only five regiments and a couple of separate battalions (one artillery and one infantry) by the following August.
Marine commitments, however, remained heavy. The brigades in both Haiti and the Dominican Republic had their hands full suppressing new rebellions. Guard detachments were still needed for Navy bases and Navy ships. The number of men required for the latter duty had fallen by only 10% since 1918. The Marines also had to staff their own bases at Quantico, Parris Island, and San Diego and they had to find men to rebuild the advance base force as well. When these facts were brought to the attention of Congress in 1920 the latter increased the Marine Corps’ authorized strength to 1,093 officers and 27,400 enlisted but then approved funding for only 20,000.
[…]
The bulk of the Corps’ operating forces were still engaged in colonial police work in the Caribbean. However, the new Commandant, Major General John A. Lejeune, was prescient enough to realize that this would not last and that a much more permanent mission would be needed to secure his service’s future. Instead, Lejeune and his advisors concluded that the real mission of the Marine Corps was “readiness”. While this concept might seem trite, one should consider that the United States was and is primarily an insular power. Its standing army in 1920 served primarily as a garrison force and cadre for a much larger wartime citizen army. Little or none of it would be available for immediate use upon the outbreak of a major war beyond the troops already deployed to major US overseas possessions like the Philippines, Hawaii, or the Panama Canal.
Although the Army of 1920 seemed to have little idea about who its future adversaries were likely to be, the Navy had already fingered Japan as its most likely future opponent. Japan had the most powerful navy after the United States and Great Britain and Japanese-American animosity was growing. The Japanese resented the treatment of Japanese immigrants in California. Americans resented Japan’s high handed actions in China. The Japanese saw American criticism of Japan’s China policy as interference in Japan’s rightful sphere of influence. Any war fought against Japan would be primarily naval in character. However, post war disarmament treaties forbade improvements to any American fortresses west of Hawaii. The League of Nations had also mandated most of the central Pacific islands to Japanese control.
If it was to successfully engage the Japanese fleet, or to threaten Japan itself, the United States Navy would need bases in those central Pacific islands. Hawaii was too far away to be useful and the Philippines were too vulnerable to Japanese attack. Only an expeditionary force could seize and hold the central Pacific islands that the Navy needed and that expeditionary force would have to be ready to move whenever and wherever the Navy did. By staying “ready”, requiring only limited reserve augmentation and, being already under the Navy’s control, the Marine Corps would be much better positioned than the Army to provide this expeditionary force, at least during the critical early stages of the next war.*
* Heinl op cit pp. 253-254; Moskin op cit pp. 219-222; and Clifford op cit pp. 25-29 and 61-64.
