After North Korea invaded South Korea on 25 June 1950, United States armed forces fought to repel Communist aggression. President Harry Truman and his advisors, not wanting the conflict to escalate into World War III, had major concerns about mobilizing reserve forces, but ultimately decided that it was a military necessity and authorized mobilization in 19 increments beginning in July 1950. Hundreds of Army and Air National Guard units were mobilized, including the 40th Infantry Division of the California Army National Guard. The "Sunshine Division" mustered into Federal service 1 September 1950 at Camp Cooke, later renamed Vandenberg Air Force Base, California. The 40th Division deployed to Japan in the spring of 1951 and trained there for months while senior Army commanders debated employing the division in Korea as a unit or as individual replacements. Eventually, in January 1952, the 40th arrived in Korea and relieved the 24th Infantry Division in place, assuming control of its positions and equipment. By 1952 the war had evolved into static defensive combat of trench and bunker warfare and small unit patrolling. The 40th Division fought mostly in platoon and company actions in the Kumsong and Kumwha Valley sectors. Though relatively minor compared to earlier battles in Korea, these small unit actions were often violent and intense. Because of the delays in deploying to Korea, many of the original California Guardsmen began to rotate home in the Spring of 1952 and were replaced by draftees. By July only a few Guardsmen remained in Korea. The 40th fought at Heartbreak Ridge and was defending the northern edge of the "Punchbowl" as the armistice came in July 1953. Today's 40th Infantry Division of the California Army National Guard carries the Lineage and Honors of the "Sunshine Division" from the Korean War.