The first major surprise of the post World War II years came into play when in late June 1950, the United States found itself responding in crisis fashion to the North Korean invasion of the new republic of South Korea, just four years and nine months after VJ-Day. The nation became involved in Korea as a result of the Cairo and Yalta conferences in which the United States and the Soviet Union agreed to the concept of a free and independent post-war Korea. Included in the agreement was a joint occupation of the country by the two powers, with the Soviets north of the 38th Parallel and the United States south. The concept of the occupation had a general objective of settling down Korea for a period so that it could learn to govern itself as a nation after many decades of Japanese rule. As the United States was painfully learning, however, it soon became apparent that what the Soviets said was one thing and what they intended was quite another with respect to a free, independent, and democratic Korea. When in 1948, they refused to participate in elections, supervised by the United Nations to form the first National Assembly, the hopes for a united Korea died. The Soviets formed a separate Communist state in their sector, the People's Democratic Republic of Korea. With the elections completed for the National Assembly in the south, the Republic of Korea (ROK) was established and the United States trusteeship in the country came to an end. The main text of this manuscript is derived from Major General John P. Condon's original draft of a history of Marine Corps aviation, an edited version of which appeared as US. Marine Corps Aviation, the fifth pamphlet of the series commemorating 75 years of Naval Aviation, published by the Deputy Chief of Naval Operations (Air Warfare) and Commander, Naval Air Systems Command in 1987. This manuscript is one in a series devoted to U.S. Marines in the Korean War era, and is published for the education and training of Marines by the History and Museums Division, Headquarters, U.S. Marine Corps, Washington, D.C., as part of the U.S. Department of Defense observance of the 50th anniversary of that war.