The people of San Diego welcomed the 4th Marine Regiment back to California from Santo Domingo, on 25 August 1924. Soon absorbed into the forces of the 5th Brigade, the personnel strength of the regiment declined as enlistments ended and personnel left the ranks. The base commander, Colonel John T. Myers, detailed some of the retumees to support the two undersized companies of the base force(1).

The postwar reduction of all branches of the armed forces had its effect upon the San Diego based regiment by causing a reduction in personnel strength. Unrest in China, with the terror of Civil War, aroused diplomatic concern for American lives in that country. This resulted in an alert for marines to be prepared for expeditionary service in China. The Commandant of the Marine Corps, on 19 September 1924, ordered an increase in personnel for the 4th Marine Regiment. The reduced level of 26 officers and 653 men would be raised to 42 officers and 1,000 enlisted marines(2).

As the tension of possible deployment overseas increased, every day saw a busy training schedule for the San Diego Marines. At the Marine Base several new areas had to be developed to provide for training in bayonet, entrenchment practice, and crew served weapons drill. The "Dutch Flats" area, now filled and leveled, provided adequate space for the conduct of training. By 10 October, the regiment's Command Officer, Colonel Alexander S. Williams, reported the 4th Marines ready to go. The orders for China service were nevertheless revoked on 15 October, disappointing many of the regiment. They resumed garrison duty at the Marine Base with at least a higher state of training to show for the alert efforts(3).

Shortly after the China alert had been cancelled, the San Diego Marines received the usual post-build up reduction. This time the ax fell upon the 4th Marines with a vengeance. By 31 October, only sixteen days after the stand down order, the strength of the regiment had been reduced to 34 officers and 765 men. This proved to be only the beginning. Dispatching men to fill other base requirements shared the credit for reduction with Congressional force cuts. By 30 September 1925, the 4th Marines could muster only 44 officers and 493 enlisted. The requirement to train and to maintain a posture of readiness for service, however, remained in effect(4).

Violence and robbery brought a new and entirely different role for the 4th Marines as the year 1926 progressed. In Elizabeth, New Jersey, on 14 October 1926, the brutal robbery and killing of a U. S. Mail truck driver forced President Calvin Coolidge to turn to the Marine Corps for assistance in the civil community. By Presidential Order, 2,500 Marines proceeded on duty to guard the mail(5). The Commandant, anticipating the Presidential Order, on 18 October had directed the Commanding General, Headquarters, Department of the Pacific, located in San Francisco,

...You will organize a force from the 4th Regiment, to be known as the Western Mail Guards, under the command of Brigadier-General Smedley D. Butler...(6)

Brigadier-General Smedley D. Butler, known as "Ol' Gimlet Eye" to fellow Marines, brought a long record of combat leadership and two Congressional Medals of Honor to the Mail Guards. Veteran of both World War I and the guerilla wars of Central America, Butler's easy-going manner hid his cold, methodical approach to the task given to the Marines. As the primary source of personnel for the Western Mail Guard, the 4th Marines initially would be spread throughout eleven states(7). Part of a twelfth state, Texas would be added on 22 October 1926. General Butler's fully armed Marines soon became sobering influences throughout Post Offices, mail trains, and mail trucks in those areas. While Marines carried out their mail guard assignment, only one attempted robbery was recorded. That particular robbery involved an unguarded mail train carrying no mail at the time. Meanwhile, in San Diego, the base stood relatively empty with a reduced level of caretaker personnel awaiting the retum of the 4th Regiment(8).

When normal operations returned to the U. S. Mail system as a result of the Marine guards, the need for continued assignment of such forces became less and less justified. The return of the 4th Marines to San Diego began on 10 January 1927 and by 18 February all personnel had been returned to their home bases as the Mail Guard Force disbanded. In 1927, American interests and lives in China and Nicaragua had once again been endangered by internal unrest and civil war. The Marines received the call to conduct expeditionary protective operations in these two countries to protect Americans and their property. The east coast based 2nd Brigade sailed for Nicaragua while the 4th Marines re inforced, becoming the 3rd Brigade under Brigadier-General Butler in San Diego, prepared for China service(9).

Many of the 4th Marines arrived back at Marine Base San Diego to find that their regiment had sailed for China on 3 February 1927. Under command of Colonel Charles S. Elill, the China- bound units assembled in and embarked from San Diego in the largest operation conducted at the San Diego Marine Base prior to World War II. The 3rd Brigade, headquartered in Shanghai, China, continued to receive reinforcements until the final movement of forces sailed from San Diego on 7 April 1927. More than 4,000 Marines had been staged through the Marine Corps Base, San Diego(10). As a direct result of the overseas force requirement, the base would be short of personnel for several years to follow. Though San Diego still claimed to be the permanent home of the 4th Marine Regiment, the base and the regiment would not be united again. The outbreak of World War II for America would find the 4th Marines still in the Orient, in the Phillipines at Subic Bay. The regiment had sailed from Shanghai and China service on 28 November 1941(11). The China service of the San Diego based Marine Regiment had lasted for just over fourteen years and nine months. The drain that this had caused on stateside bases and forces would see no change until the forces in Nicaragua returned. Until these Marines returned, the San Diego Marine Base would continue to be operating at a reduced force level(12).

The Marine Base in San Diego, in the 1930's, played a major part in the Marine Corps' evolutionary steps towards development as an amphibious force. By mid-1933, the last of the 2nd Marine Brigade had been withdrawn from Nicaragua. At that time personnel became available for a major reorganization within the Marine Corps. Specifically, the Marine mission and its relationship with the Navy in accomplishment of that mission. Major-General Benjamin H. Fuller, Commandant of the Corps, began the actions which resulted in Navy Department General Order No. 241, on 7 December 1933. With that order the Fleet Marine Force became a reality, placing that force as an integral part of the fleet. Now the Marine Corps had finally and totally committed itself to the doctrinal position that in time of war, the mission of the Marines would be to serve the fleet by seizing and holding advanced bases for naval operations. In peacetime, the Marine Corps would be primarily concerned with preparation for the successful accomplishment of the wartime assignment(13).

The Fleet Marine Force initially had two main components, one on the east coast at Quantico, Virginia, and the other on the west coast, at San Diego. As the new and innovative force progressed through its formative years, 1933 to 1934, the headquarters remained at Quantico, near Marine Headquarters in Washington, D. C. In 1935, Major-General John H. Russell, the Commandant, caused the Headquarters, Fleet Marine Force to be relocated at the Marine Base San Diego. As a major proponent of the Marine role in amphibious warfare, General Russell had been the drafter of Navy Department Order No. 241. As the force developed, he became convinced that the headquarters should be located as near as possible to the fleet. Since the bulk of the U. S. Fleet operated from west coast bases, the force move seemed appropriate. Headquarters, Fleet Marine Force transferred to the Marine Corps Base, San Diego, in September 1935(14).

With the establishment of the Fleet Marine Force, the east and west coast forces for operation, in 1935, received the status of brigades. The east coast force became the 2nd Brigade and the west coast units formed the 1st Brigade. As of 30 June 1935, the 1st Brigade in San Diego consisted of the 6th Marine Regiment, less 3rd Battalion, the 2nd Battalion (less Battery F) of the 10th Marines (Artillery), and Aircraft Two, (Squadron 2)(15). Later as war approached, the 1st and 2nd Brigades became the 1st and 2nd Marine Divisions in February 1941(16).

While it might seem that the Marine Base, San Diego, served throughout the 1930's only in support of operating forces, this is incorrect. As the expeditionary forces assembled and debarked, and as the Fleet Marine Force came into being, the Marine Base also had been functioning in the less visible half of its dual function -- as a recruit training depot. This task had been an active role for the Depot since 1923, when recruit training had come to San Diego from Mare Island(17).

The recruit training period of the base's early years varied from time-to-time. Since the essentials of the training did not change, however, a look at recruit training in the 1923 to 1936 period will show the nature of the instruction. In 1932, the course lasted eight weeks. Courses varied from instruction in Marine Corps Customs and History to the specific skills of the combat Marine. After the eight weeks of basic training, selected recruits then attended a four week Sea School where they received addi- tional training to prepare them for duty aboard the ships of the fleet. The Sea School was organized in 1923 and, like the Recruit Training Depot, remains an important part of the Marine Base in 1974(18).

The Marine Base functioning in the 1926 to 1940 period had been an active succession of events requiring rapid response. This period of the base's history also involved physical growth as well. The drill field of the base, for example, had an original size of 1275 feet by 210 feet and consisted of soft green grass. Easy-on- the eye but hard to maintain as the recruits' boots ground into the turf, the field had to be paved in late 1929. Later paving require- ments occurred when a small addition to the field came about in 1930 and again in 1935 and 1936. In those latter years, the present size of the drill field was achieved. The size increased to 2550 feet by 509 feet or 29.90 acres(19). While the drill field, "grinder" as it is called, underwent changes, no other major con- struction occurred. The period 1926 to 1940 saw many functional and unit modifications, however, war year requirements would be needed to bring about more major construction. Emergency ex- pansion of base facilities began in September 1939, the month in which World War II broke out in Europe.