As a high school student, he captained the football team, played hockey, and won the Queen's Badge for his activities in the Boys' Brigade.
After Singapore's independence from Malaysia on 9 August 1965, Choo, then the battalion signals officer, was appointed as a military aide to President Yusof Ishak.
He attended the US Army Command and General Staff course at Fort Leavenworth in Kansas, United States, that following year, and graduated with distinctions in all his subjects.
In the same year, he was named an honorary aide-de-camp to President Benjamin Sheares,[1] and took up the command of the 2nd Singapore Infantry Brigade (2 SIB).
In 1981, he went to the United States to study for a master's degree in military history at Duke University[6] and returned to Singapore in 1982 to resume his post as the Chief of General Staff.
He retired from the SAF on 30 June 1992, after which he went to Harvard Business School and attended the six-week Advanced Management Program.