Major Guillermin was assigned to the 609th Air Commando Squadron in South East Asia during the Vietnam War. Louis joined the Air Force as an Aviation Cadet. He received his pilots training at Lackland Air Force Base in San Antonio, Texas. Louis received further training in radar and celestial navigation instruction at Connelly Air Force Base in Texas. He was commissioned as a Second Lieutenant and awarded his silver wings in April 1964.

Major Guillermin was assigned to the 609th Air Commando Squadron in South East Asia during the Vietnam War. Louis joined the Air Force as an Aviation Cadet. He received his pilots training at Lackland Air Force Base in San Antonio, Texas. Louis received further training in radar and celestial navigation instruction at Connelly Air Force Base in Texas. He was commissioned as a Second Lieutenant and awarded his silver wings in April 1964.