Sergeant Major Fabian Casillas reported to Marine Corps Recruit Depot, San Diego on October 7, 1992. He graduated on December 31, 1992. Upon graduation from MCT, he reported to MCSSS, Camp Lejeune, North Carolina for instruction in Basic Motor Transport Maintenance. Upon successful completion, he received orders to 3D FSSG, Okinawa Japan.
In June of 1993, Private First Class Casillas reported for duty to 9th Motor Transport Battalion, Camp Foster, Okinawa, Japan, where he served as an organizational mechanic in both the preventive maintenance and corrective maintenance sections.
In January, 1994 Lance Corporal Casillas reported to 1st Maintenance Battalion, 1st FSSG, Camp Pendleton, California for service as an organizational mechanic. While assigned to this unit, he performed duties as a mechanic, a marksmanship instructor, and platoon sergeant for Motor Transport Engineer Platoon. He was promoted to the ranks of Corporal and Sergeant during this time.
In January of 1998, Sergeant Casillas attended and graduated from Drill Instructor School, MCRD San Diego and was subsequently assigned to 1st Recruit Training Battalion, Bravo Company for duty as a Drill Instructor. Sergeant Casillas completed 5 cycles. He was promoted to the rank of Staff Sergeant in March of 2000.
After a successful tour as a Drill Instructor, Sergeant Casillas opted to leave active duty and transferred to the Selected Marine Corps Reserves. In June of 2000, Staff Sergeant Casillas reported to Marine Wing Communication Squadron-48 for duty as a drilling reservist, serving as the Motor Transport Maintenance Chief. In March of 2003, Staff Sergeant Casillas was mobilized and deployed in support of Operation IRAQI FREEDOM. In the summers of 2004 and 2005, Staff Sergeant Casillas performed active duty as a Sergeant Instructor for Officer Candidate School.
Upon completion of his duties as a Sergeant Instructor, Staff Sergeant Casillas accepted mobilization orders to serve as the West Coast Injured Support Coordinator for HQMC. This assignment evolved into almost four years of continuous mobilization during which time he was promoted to the rank of Gunnery Sergeant and saw the transition from Marine-4-Life Injured Support to the Wounded Warrior Regiment. He completed his tour of duty in February of 2009.
Gunnery Sergeant Casillas augmented back into the active duty forces in February of 2009. He received orders to 1st Battalion, 11th Marines where he served as the Motor Transport Maintenance Chief. In March of 2010, Gunnery Sergeant Casillas deployed in support of Operation ENDURING FREEDOM, Helmand Province, Afghanistan.
In May of 2011, Gunnery Sergeant Casillas received orders to Marine Wing Headquarters Squadron, 3d Marine Aircraft Wing to serve as the G-4, Motor Transport Maintenance Chief. In December of that year, he was selected to the rank of First Sergeant and frocked on April 13, 2012.
First Sergeant Casillas reported to 1st Law Enforcement Battalion in April of 2011. He served as the Company First Sergeant for both Alpha Company and Headquarters and Support Company.
First Sergeant Casillas checked into 1st Battalion, 4th Marines, in January of 2015 and served as the Company First Sergeant for Company A during the MRF- D deployment to Darwin, Australia and Company C for the 11th Marine Expeditionary Unit deployment. He was selected for Sergeant Major and frocked in June of 2017.
He served as the Squadron Sergeant Major for Headquarters and Headquarters Squadron, MCAS Yuma from July 2017 to July 2019 and then as the Squadron Sergeant Major for Marine Wing Communication Squadron - 38 from August 2019 until January 2021. From January 2021 to July 2023 he served as the Regimental Sergeant Major for the Recruit Training Regiment, MCRD, Parris Island. Sergeant Major Casillas is married to the former Christina M. Meneses Ed. D., and together have three children.
Sergeant Major Casillas' personal decorations include the Meritorious Service Medal with two gold stars in lieu of third award, Navy Commendation Medal with three gold stars in lieu of fourth award, Navy and Marine Corps Achievement Medal.