Sergeant Major Monssen graduated from Thomas Jefferson High School in June 1988, he than reported to Marine Corps Recruit Depot San Diego, California, for recruit training. Sergeant Major Monssen graduated in September as a Private First Class and received orders to Aviation Logistics School, Meridian, Mississippi. After completion of his primary military occupational specialty school, he proceeded to his first assignment at Marine Corps Air Station Tustin, California.
In December 1988, Sergeant Major Monssen reported to Marine Aviation Logistics Squadron 16, Marine Aircraft Group 16, 3d Marine Aircraft Wing. During this time he was promoted to Lance Corporal and completed a 13th Marine Expeditionary Unit deployment in 1989 with Marine Medium Helicopter Squadron-166 (Reinforced) aboard the USS PELELIU. Upon completion of this deployment, he deployed in support of Operation DESERT SHIELD/DESERT STORM with Marine Medium Helicopter Squadron 268 (Reinforced), 5th Marine Expeditionary Brigade aboard the USS NEW ORLEANS and was promoted to Corporal. He then deployed again in support of Operation DESERT STORM with Marine Heavy Helicopter Squadron 361 to support naval vessels within the region. In 1992, he deployed to Mogadishu, Somalia, in support of Operation RESTORE HOPE with Marine Aircraft Group 16 (Forward).
In March 1993, Sergeant Major Monssen received orders to Marine Aircraft Group 42, Detachment Bravo. There he received his Aerial Observer/Gunner certification in the CH-46E Sea Knight. On 1 March 1995, he was promoted to Sergeant and, in November of 1995, attended the Sergeants Course at Quantico, Virginia. In April 1996, he attended Drill Instructor School, Marine Corps Recruit Depot San Diego, California and upon graduation was assigned to Company K, 3d Recruit Training Battalion, Recruit Training Regiment, where he served as a Drill Instructor and Senior Drill Instructor.
After Sergeant Major Monssen’s successful tour on the drill field, he was transferred to Marine Aviation Logistics Group 11, Marine Aircraft Group 11, 3d Marine Aircraft Wing, Miramar, California. In January of 2000 he then deployed in support of Operation SOUTHERN WATCH with VMFA-121. In September 1998, he was promoted to the rank of Staff Sergeant. In October 2000, he reported to Marine Wing Headquarters Squadron 1 as an Inspector for the Aviation Wing Supply Assist Team. In January 2002, he was promoted to Gunnery Sergeant and attended the Advanced Course at Camp Pendleton, California.
In June 2002, Sergeant Major Monssen reported to Marine Aviation Weapons and Tactics Squadron 1, Yuma, Arizona, as the Aviation Logistics Chief/S-4 Chief. Following selection to First Sergeant in December 2005, he was frocked 30 January 2006, and transferred to Battery G, 2d Battalion, 11th Marines, 1st Marine Division, Camp Pendleton, California as the Battery First Sergeant. In March 2006, he deployed to Fallujah, Iraq with Regimental Combat Team 5 in support of Operation IRAQI FREEDOM. Upon his return, Battery G was assigned to Battalion Landing Team 1/5, where he deployed with the 11th Marine Expeditionary Unit from November 2007 to June 2008 aboard the USS TARAWA. In February 2009, Sergeant Major Monssen reported to Company I, Marine Combat Training Battalion, School of Infantry East as a Company First Sergeant. Sergeant Major Monssen was promoted to his present rank March 2010 and reported to Infantry Training Battalion on 29 March 2010.
In October 2011, he relinquished his post and reported to 3d Battalion, 9th Marines as the Battalion Sergeant Major. In October 2012, Sergeant Major Monssen deployed to Helmand Province, Afghanistan, in support of Operation ENDURING FREEDOM. Upon return, 3d Battalion, 9th Marines was deactivated on 13 August 2013. In September 2013 Sergeant Major Monssen reported to Marine Aircraft 31 as the Group Sergeant Major and in May 2015 relinquished his post.
In June 2015, Sergeant Major Monssen assumed his duties as the Training Command Sergeant Major.
Sergeant Major Monssen’s personal decorations include the Bronze Star Medal, Meritorious Service Medal with gold star in lieu of second award, Navy and Marine Corps Commendation Medal with four gold stars in lieu of fifth award, Navy and Marine Corps Achievement Medal with one silver star in lieu of sixth award, Combat Action Ribbon, and the Military Outstanding Volunteer Service Medal.