Training requirements for the San Diego Fleet Marine Force units resulted in the need to obtain more land. In 1934, in anticipation of the need, land in the Kearny Mesa section of San Diego had become known after World War I as Camp Holcomb, named after the then Commandant, Major-General Thomas Holcomb.
Camp Holcomb was constructed as part of Camp Kearny, a World War I Army camp, where both the 40th and 16th Divisions had trained. By 1940, volunteers began to pour into the recruit training depot at the San Diego Base. To provide needed space for recruit training expansion, the Fleet Marine Force units moved from the San Diego Base to the camp in the Kearny Mesa area. Applied collectively to the many semi-permanent buildings constructed in the area, Camp Holcomb would be only temporary.
The camp's name was not popular with Major General Holcomb, due to the military's custom of never naming an installation or ship after a living person, and on June 14, 1940 the installation was formally redesignated Camp Elliot in honor of Major General George F. Elliot, the Marine Corps tenth Commandant 1903-1910.
While construction was underway the Marines had to live in tents. Early construction progressed quite well and by October 1940 twelve barracks and a mess hall was completed. Additional land acquisition for Camp Elliot was accomplished through a Declaration of Taking on April 8, 1941- Including the main camp area of 19,298.25 acres which came under federal ownership. This was further expanded to 26,034 acres.
In September 1942, Camp Elliot became the home of the Fleet Marine Force Training Center, West Coast with the mission of training individual replacements for combat duty. In January 1942, with over 10,000 Marines in the San Diego area, the 2nd Marine Division, under the command of Major-General C. F. B. Price, assembled at Camp Elliot and assumed the responsibility for the conduct of the training there. Although thousands of Marines passed through Camp Elliot enroute to Pacific duty, even this area could not meet the expansion needs for the training of the overseas replacements.
In addition to the main Camp area there were other training camps established on the Camp Elliot Naval Reservation Camp Linda Vista, Green Farm Camp and Jacques Farm Camp, as well as a Parachute School. Naval records also indicate that a Naval Training and Distribution Center was located on the reservation.
Camp Elliot, on 1 July 1946, became War Assets Administration Property for disposal and decommissioning. Portions of this training area came under Navy control and, in 1944, the Navy took over Camp Elliot from the Marines, who were later transferred to Camp Pendleton.
Following World War II, the property served a variety of temporary uses including use as the headquarters for the California Army National Guard's 251st Anti-Aircradt Artillery Group as well as an illegal immigrant detention camp operated by the Immigration and Naturalization Service. With the onset of the Korean conflict, the Navy reactivated Camp Elliot as Naval Training Center Elliott Annex. It served as an auxiliary training center from 1951 to 1953 for additional recruits from NTC San Diego. In 1960, the Camp was decommissioned and was divided between NAS Miramar and the Air Force for the creation of the Atlas Missile test facility. Sycamore Annex was developed by General Dynamics under direction of the National Aeronautics and Space Administration (NASA) as a high security testing area used in the development of the Atlas and Centaur missiles. In 1966, the facility was transferred to NASA and by 1969, the site was classified as surplus property and title was transferred to the General Services Administration. In December 1972, the parcel was transferred to the Navy, to be included in the NAS Miramar property.