After recruit training, Thetford reported to Artillery Training School aboard Marine Corps Base Camp Pendleton, Calif., for the Cannon Crewman Course.

He returned home to Texas and spent the next three years serving with 2nd Battalion, 14th Marines, where he attained the rank of sergeant.

Thetford volunteered in April 1984 for Extended Active Duty to be augmented to a recruiting substation. He served both as a canvassing recruiter and staff noncommissioned officer-in-charge of a substation.

After augmenting to full time active duty in August 1987, Thetford was transferred to Marine Corps Air Ground Combat Center, Marine Air Ground Task Force Training Command, Twenty Nine Palms, Calif. There he was assigned to 5th Battalion, 11th Marines and spent the next three years as a Gun crew chief training and supporting operations in the desert of Twenty Nine Palms.

Later in 1990, Thetford volunteered for duty as a drill instructor and attended school aboard Marine Corps Recruit Depot San Diego, Calif. After successfully completing the course he was assigned to Lima Company, 3rd Recruit Training Battalion. While still serving as a drill Instructor, Thetford was augmented to I Marine Expeditionary Force, 10th Marines, in support of Operation Desert Storm.

After returning from his overseas combat tour, he returned to San Diego to finish his tour as a drill instructor. Next he was transferred to the Army Field Artillery Center aboard Fort Sill, Okla., in July 1992 where he served as an artillery instructor. In November of the same year he was selected for promotion to staff sergeant.

Once again Thetford volunteered for recruiting duty and was sent to Recruiting Station San Antonio, Texas, Recruiting Substation Austin South, where he was the SNCOIC. In July 1997 Thetford was selected for meritorious promotion to gunnery sergeant and was sent to the recruiting station headquarters to be the pool coordinator.

In August 1998, Thetford moved onto Marine Corps Base Camp Pendleton, Calif., and was attached to the 11th Marines in the 1st Marine Division. There he served as the battery gunnery sergeant for Headquarters and Support Battery and Romeo Battery 5th Battalion 11th Marines. While attached to the 11th MEU and Battalion Landing Team 2nd Battalion, 1st Marines, he was selected for promotion to first sergeant in 2001 and reassigned to 3rd Battalion, 5th Marines.

As the first sergeant for Weapons Company, 3/5, he deployed to Iraq in support of Operation Iraqi Freedom. After returning home in 2003 he was reassigned to H&S Company, 3/5, and was redeployed in September of 2004 where his battalion participated in the battle of Fallujah.

After returning home in April of 2005, Thetford was transferred to the Mobilization Support Battalion as the acting sergeant major. Thetford was subsequently selected for promotion to sergeant major in November 2005.

After his stay aboard Camp Pendleton, he returned to recruiting to serve as the Sergeant Major for Marine Corps Recruiting Station Columbia, S.C., in the 6th Marine Corps District.

After completing his tour in Columbia, Thetford reported to Marine Corps Air Station Beaufort where he was appointed as VMFA-(AW) 533 Sergeant Major. He then deployed to Marine Corps Air Station Iwakuni, Japan for six months under the Unit Deployment Program.

Thetford was appointed the 6th Marine Corps District Sergeant Major on November of 2011.

His personal decorations include the Navy Commendation Medal, Army Commendation Medal, Navy Achievement Medal with 3 gold stars, Army Achievement Medal, Meritorious Service Medal, and Combat Action Ribbon.