When the communist North Korean Army invaded South Korea on June 25, 1950, MacArthur sent Church to lead a survey team of staff officers to work with Ambassador Muccio and the Korean Military Advisory Group and assess what assistance could be provided to the South Korean Army. This task resulted in the establishment of GHQ Advance Command and Liaison Group at Suwon. Arriving in Korea on June 27, in his role as commander of ADCOM, Church worked with the Chief of Staff of the South Korean Army, General Chae Byung-dok, to improve the South Korean defensive arrangements. Despite his efforts, Seoul was captured by the North Koreans on 28 June and Church recommended the deployment of at least two combat teams of U.S. personnel to help stabilise the situation. This prompted MacArthur to undertake his own survey in Korea the following day and after a further report from Church, he committed U.S. forces to Korea, having received permission from President Harry Truman to do so. Accordingly, the 24th Infantry Division, which was stationed in Japan as part of the U.S. Eighth Army, was the first army unit sent over from Japan under the command of Major General William F. Dean. A reinforced company of the division, commanded by Lieutenant Colonel Brad Smith, was sent north from Pusan to try to halt the North Koreans. Meeting with Smith at Taejon, Church informed him "All we need is some men up there who won't run when they see tanks", and instructed Smith to make his stand at Osan. Task Force Smith was without tank support and had faulty communications, and was promptly overrun in its first engagement with the North Koreans. Dean gathered his troops in the city of Taejon and formed a strong defense. After a stubborn fight, the American troops retreated. Dean got separated from his troops and was captured. On July 22, Church, without a command following the dissolution of ADCOM, was given command of the division. His new command was given a two-day period to rest, but then Lieutenant General Walton Walker, the commander of the U.S. Eighth Army, decided that he needed the 24th to guard the Southwest line of the Pusan Perimeter. During the subsequent battle, the North Korean 6th Division inflicted more losses on Church's men and gradually pushed the 24th back. Finally, Church by now promoted to major general, was able to regroup his men, and they held the perimeter, especially with the help of a brigade of marines. Frail and suffering from arthritis, Church remained in command of the 24th until January 25, 1951. His health meant that he was not often in the field and Lieutenant General Matthew Ridgway, commander of the U.S. Eighth Army following the death of Walker in December 1950, considered this was detrimental to the state of the division. Ridgway relieved Church of his command and replaced him with Brigadier General Blackshear M. Bryan. Church was awarded the Army Distinguished Service Medal for his leadership of the 24th Division while in Korea.
Later life
Church subsequently was appointed commandant of the U.S. Army Infantry School at Fort Benning, Georgia and served in that capacity until his retirement from the military in June 1952. He died on 3 November 1953 in Washington, D.C. Survived by his wife, he was buried in Arlington National Cemetery, in Virginia.