Sergeant Major Underwood enlisted on 19 October 1998 and attended recruit training at MCRD, San Diego, California. Upon graduation of recruit training, he was promoted to Private First Class and attended Marine Combat Training at Camp Pendleton. Sergeant Major Underwood reported on 14 February 1999 to Marine Aviation Training Support Group 21, Pensacola, Florida for the Aviation Support Equipment Technician course. He was promoted to Lance Corporal 1 July 1999 and then graduated 3 August 1999. He reported to Naval Air Station North Island, California, where he attended the Support Equipment Engine/Gas Turbine Intermediate Maintenance course, graduating on 18 February 2000, and obtaining the MOS of 6072, Ground Support Equipment Mechanic.
Sergeant Major Underwood reported on 4 March 2000 to Marine Aviation Logistics Squadron 14, Cherry Point, North Carolina for duty as a Support Equipment Technician. He was promoted to Corporal on 1 May 2000. In March 2001, Sergeant Major Underwood deployed to Marine Corps Air Station Iwakuni, Japan as an augment to VMAQ-2's Unit Deployment Program. He was promoted to Sergeant on 1 October 2001 and from August 2002 to May to 2003, he deployed as an augment with HMM-263 as part of the 24th Marine Expeditionary Unit aboard the USS Nassau in support of Operation Enduring Freedom and Operation Iraqi Freedom. Throughout his tour at Cherry Point, Sergeant Major Underwood served as a Work Center Supervisor and Collateral Duty Inspector. On 1 February 2005 he was promoted to Staff Sergeant and reported to Basic Recruiter Course at MCRD San Diego on 26 February 2005. After graduation, he was assigned to Recruiting Station Fort Worth, Texas where he served as a canvassing recruiter and MEPS Liaison.
Upon successful completion of recruiting duty, Sergeant Major Underwood executed orders to Marine Aviation Logistics Squadron 24, Kaneohe Bay, Hawaii on 16 May 2008 where he served as shift supervisor. In January 2009 he deployed to Al Asad Airbase, Iraq where he served as Training SNCOIC and then Kandahar, Afghanistan as the night crew SNCOIC. Upon his redeployment to Kaneohe Bay, Hawaii in August 2009, he served as a Quality Assurance Representative. On 25 June 2011 Sergeant Major Underwood executed orders to Marine Aviation Training Support Group 21, Pensacola, Florida for duty as an “A” school instructor and was promoted to Gunnery Sergeant on 1 July 2011. He served as a hydraulic systems instructor, diesel engine maintenance instructor, Course Supervisor, and Aviation Support School SNCOIC.
Sergeant Major Underwood reported for duty at MALS-39, Camp Pendleton, California on 6 June 2014 where he served as the Squadron Legal Officer, and Support Equipment Division SNCOIC. Sergeant Major Underwood was promoted to First Sergeant on 17 January 2017 and reported to 3d Battalion, 5th Marines where he was assigned as the Lima Company First Sergeant. From May to November 2017 he deployed with the 31st Marine Expeditionary Unit aboard the USS Greenbay and then transferred to Weapons Company in January 2018. He deployed with the 11th Marine Expeditionary Unit aboard the USS John P. Murtha, from April to November of 2019 and then reported to Marine Corps Engineer School, Camp Lejeune, North Carolina on 21 February 2020 where he served as the Utilities Instruction Company First Sergeant.
On 20 May 2021, Sergeant Major Underwood was promoted to his current rank and reported to Marine Corps Air Station New River, North Carolina where he currently serves as the Headquarters and Headquarters Squadron Sergeant Major.
Sergeant Major Underwood's personal awards include the Navy and Marine Corps Commendation Medal and the Navy and Marine Corps Achievement Medal with 3 gold stars. He holds a Bachelor of Arts degree in History, suma cum laude.