Lieutenant Colonel Brennan Simi graduated from Texas Christian University and was commissioned a Second Lieutenant in August 2004 after completing Officer's Candidate School. From August 2004 to August 2005, he attended The Basic School in Quantico, Virginia and the Field Artillery Officer Basic Course at Fort Sill, Oklahoma.
From September 2005 to June 2008, he served as an Artillery Forward Observer, Liaison Officer, and Guns Platoon Commander for Echo Battery, 2d Battalion, 10th Marines, 2d Marine Division. During this period, he deployed with Echo Battery, 3d Battalion, 14th Marines, Task Force Military Police to Operation IRAQI FREEDOM 05-07.2 as a convoy security platoon commander. Then he deployed to Operation IRAQI FREEDOM 06-08.2 with 2d Combat Engineer Battalion, Task Force Guardian as a provisional infantry platoon commander in Al Fallujah, Iraq.
In June 2008, First Lieutenant Simi reported to 11th Marine Expeditionary Unit in Camp Pendleton, California, and assumed the responsibilities of Target Information Officer and Information Operations Officer. During this period, he deployed to the Pacific and Central Commands’ Area of Responsibility as part of the MEU’s WESTERN PACIFIC 09-2 deployment.
From February 2011 to October 2011, Captain Simi attended Field Artillery Captain’s Career Course in Fort Sill, Oklahoma.
In October 2011, Captain Simi reported to 1st Battalion, 12th Marines, 3d Marine Division at Marine Corps Base Kaneohe Bay, Hawaii. He immediately assumed duties as the Operations Officer for Combined Arms Training Center, Camp Fuji, and upon return assumed command of Bravo Battery 1st Battalion, 12th Marines. After battery command, he assumed the duties of Battalion Logistics Officer, and Battalion Operations Officer.
In July 2015, Major Simi reported to 3d Battalion, 12th Marines, 3d Marine Division in Okinawa, Japan, and assumed duties as the Assistant Fire Support Coordinator for 4th Marine Regiment then Battalion Operations Officer until his reassignment to Australian Command and Staff College in December 2017.
Upon completion of Australian Command and Staff College, Major Simi was selected to serve in the Personnel Exchange Program, and was assigned as an exercise planner in Australia’s Joint Operations Command in Canberra, Australia. Upon completion of his international exchange tour in September 2020, Lieutenant Colonel Simi served as the senior Fires and Effects instructor for Marine Corps Tactics and Operations Group until his selection as Inspector-Instructor for 6th Air Naval Gunfire Liaison Company, Joint Base Lewis-McChord, Washington.
Lieutenant Colonel Simi has a Masters of Arts with an emphasis in International Relations through the University of Oklahoma, and a Masters of Military and Defense Studies from the Australian National University. His personal decorations include the Navy and Marine Corps Commendation Medal with four gold stars and the Navy and Marine Corps Achievement Medal.