Lieutenant Colonel David S. Rainey was commissioned as a second lieutenant, upon graduation from the U.S. Naval Academy in May 2004. He then reported to The Basic School (TBS) in June 2004 and graduated in January 2005. After TBS, he attended the Military Police Officer Basic Course at the U.S. Army Military Police School in Fort Leonard Wood, Missouri and graduated in May 2005.
In May 2005, Second Lieutenant Rainey was assigned to Marine Wing Support Squadron (MWSS) 373 at MCAS Miramar in San Diego, California. While there, he served as the Military Police Platoon Commander. In September 2006, First Lieutenant Rainey deployed with MWSS 373 to Al Taqqadum, Iraq in support of Operation Iraqi Freedom (OIF) 05-07.2. After returning in March 2007, he was assigned as the S-3 Training Officer, where he served until September 2007.
In September 2007, First Lieutenant Rainey transferred to Fort Leonard Wood, Missouri to serve as the Officer in Charge/School Director of the Interservice Non-lethal Individual Weapons Instructor Course (INIWIC). He was promoted to Captain in July 2008 and continued to serve at INIWIC until April 2009.
In May 2009, Captain Rainey was assigned as an Individual Augment to 3rd Battalion, 24th Marine Regiment (3/24) at MCB Camp Pendleton, California. Upon arrival, he was assigned as the Executive Officer for the battalion's Weapons Company and deployed to Iraq in support of OIF 09.2 in August 2009. The unit subsequently returned to Camp Pendleton in February 2010 and completed the demobilization process. Captain Rainey returned to Fort Leonard Wood in March 2010 and assumed duties as the Academics Officer for the U.S. Marine Corps Military Police School. In July 2010, he was assigned to the U.S. Army Military Police Captains Career Course and graduated in December 2010. During this period Captain Rainey also received a Masters of Arts in Security Management from Webster University in Saint Louis, Missouri.
In January 2011, Captain Rainey transferred to the Provost Marshals Office (PMO) at MCB Quantico, Virginia and assumed duties as the Operations Officer. In July 2014, Captain Rainey transfered to the Marine Corps Command and Staff College (CSC) aboard MCB Quantico. He was promoted to Major in September 2014, before graduating from CSC in June 2015. Upon completion, Major Rainey also received a Masters of Military Studies from the Marine Corps University.
After graduating from CSC, Major Rainey reported to 1st Law Enforcement Battalion aboard MCB Camp Pendleton, California and was assigned as the Operations Officer until May 2016. In June 2016, Major Rainey was selected to serve as the Commanding Officer for Task Force Koa Moana, leading the unit in support of operations in seven different nations across the Oceania region of the Asia-Pacific. The Task Force returned to Camp Pendleton in December 2016 to complete redeployment requirements. Major Rainey returned to 1st Law Enforcement Battalion in February 2017 and resumed his duties as the Operations Officer.
In June 2018, Major Rainey was selected to attend the U.S. Army School of Advanced Military Studies (SAMS) in Fort Leavenworth, Kansas. He graduated in May 2018 and received a Masters of Arts in Military Operations. Major Rainey then transfered to the III Marine Expeditionary Force (MEF) in Okinawa, Japan. Upon arrival, he was assigned as the Korea Plans Officer within the III MEF G-35 (Future Operations Section). While there, he was promoted to Lieutenant Colonel in October 2020. In June 2021, Lieutenant Colonel Rainey transfered to MCB Quantico to assume responsibilities as the Commanding Officer for Security Battalion.
Lieutenant Colonel Rainey's personal decorations include the Meritorious Service Medal (with one gold star), Navy-Marine Corps Commendation Medal (with three gold stars), Navy Achievement Medal, Combat Action Ribbon, Iraqi Campaign Medal (with three bronze stars), and the Korea Defense Service Medal.