In 1947, Choi was promoted to captain, and then to major. In 1948, he was posted to Seoul as the head of logistics and he became a martial arts instructor for the American Military Police School in Seoul. In late 1948, Choi was promoted to lieutenant colonel. In 1949, he was promoted to full colonel and, in June, he visited the United States for the first time, attending Advanced Military Training School at the Fort Riley Ground General School in Kansas. While there, gave public demonstrations of his martial arts skills for the troops; this was the first display of Taekyon/karate in America. Choi graduated on June 23, 1950, just two days before the Korean War started, so he had to rush back to Korea where he established the Officer Training School.
Choi later attended the Advanced Command School at Fort Benning, Columbus, Georgia. At the time, Fort Benning was called the birthplace of American Infantry Corps and parachute troops; it was a requirement for all the officers to go through it. Even Field Marshall Erwin Johannes Eugen Rommel (1891-1944) of Germany, who was called the "Desert Fox" during the WWII because of his expert command in tanks in African deserts, had attended the school.
In 1951, Choi was promoted to brigadier general. During this time, he organized the Ground General School in Pusan and served as Assistant Commandant and Chief of the Academic Department. In 1952, Choi was appointed as Chief of Staff of the First Corps and was responsible for briefing General Douglas Mac Arthur the Supreme Commander of the United Nations Troops, during the latter's visits to Kang Nung. Mac Author was visiting the front line and Choi was selected to update him on the battle situation. After the thirty minutes briefing, Choi asked the general if he had any questions. To which the general replied, "No questions; very clear." He then approached to Choi and while shaking Choi's hand asked him his name. At the time of armistice in 1953, Choi was in command of the Fifth Infantry Division. The year 1953 was eventful for the Choi in both his military career and in the progress of his new martial art. He authored Military Intelligence, the first authoritative book on military intelligence in Korea.