On June 20, 1966, he enlisted in the U.S. Marine Corps Reserve. He was a member of the Special Volunteer Reserve, 1st Marine Corps District, New York, New York, until discharged to enlist in the regular Marine Corps on October 5, 1966.
After completion of recruit training at the Marine Corps Recruit Depot Parris Island, South Carolina, in December 1966, he underwent individual combat training and weapons special training with the 2nd Infantry Training Battalion, 1st Infantry Training Regiment, Marine Corps Base, Camp Lejeune, North Carolina. He was promoted to private first class, December 1, 1966, while undergoing individual combat training.
In March 1967, PFC Barker joined Marine Air Base Squadron 21, Marine Aircraft Group 12, 1st Marine Aircraft Wing, San Francisco, California, and served as group guard until the following June.
Reassigned as a machine gunner with Company F, 2nd Battalion, 4th Marines, 3rd Marine Division, in the Republic of Vietnam. He was promoted to lance corporal on September 1, 1967. Barker was killed in action on September 21, 1967, while on patrol near Con Thien.
The Medal of Honor was presented to Barker's family by Vice President Spiro Agnew in ceremonies held on October 31, 1969.
PFC Barker was buried at the George Washington Memorial Park in Paramus, New Jersey.
Barkers medals and decorations include: the Medal of Honor, the Purple Heart, the Presidential Unit Citation, the National Defense Service Medal, the Vietnam Service Medal with one bronze star, and the Republic of Vietnam Campaign Medal.
For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty while serving as a machine gunner with Company F, Second Battalion, Fourth Marines, Third Marine Division, in the Republic of Vietnam on 21 September 1967. During a reconnaissance operation near Con Thien, Corporal Barker's squad was suddenly hit by enemy sniper fire. The squad immediately deployed to a combat formation and advanced to a strongly fortified enemy position, when it was again struck by small arms and automatic weapons fire, sustaining numerous casualties. Although wounded by the initial burst of fire, Corporal Barker boldly remained in the open, delivering a devastating volume of accurate fire on the numerically superior force. The enemy was intent upon annihilating the small Marine force and, realizing that Corporal Barker was a threat to their position, directed the preponderance of their fire on his position. He was again wounded, this time in the right hand, which prevented him from operating his vitally needed machine gun. Suddenly, and without warning, an enemy grenade landed in the midst of the few surviving Marines. Unhesitatingly and with complete disregard for his own personal safety, Corporal Barker threw himself upon the deadly grenade, absorbing with his own body the full and tremendous force of the explosion. In a final act of bravery, he crawled to the side of a wounded comrade and administered first aid before succumbing to his grievous wounds. His bold initiative, intrepid fighting spirit, and unwavering devotion to duty in the face of almost certain death undoubtedly saved his comrades from further injury or possible death and reflected great credit upon himself, the Marine Corps, and the United States Naval Service. He gallantly gave his life for his country./S/RICHARD M. NIXON