LtCol Gehman graduated from the United States Naval Academy in May 1998 with a degree in Systems Engineering. Following graduation, he completed the Basic School in December 1998 and reported to NAS Pensacola for flight training. He earned his wings in May 2001 after flying T-34s with VT-3, T-2s with VT-9 and T-45Cs with VT-7. He then reported to MCAS Miramar for further training in the F/A-18 Fleet Replacement Squadron, VMFAT-101. After completing the FRS in September 2002 he was assigned to VMFA(AW)-225 at MCAS Miramar, California.
While attached to the "Vikings" of VMFA(AW)-225, LtCol Gehman served as the Classified Material Control Custodian Officer, Aviation Life Support Systems Officer, and Aviation Safety Officer. After attending Top Gun in 2004 and the Weapons and Tactics Instructor Course in 2005, LtCol Gehman served as the Pilot Training Officer. During this tour he completed one combat deployment to Kuwait in 2003 for Operation Southern Watch/Operation Iraqi Freedom and two WESTPAC deployments to Iwakuni, Japan in 2004 and 2005. While on these deployments, the squadron conducted training in Alaska, South Korea, Thailand and Okinawa, Japan.
In May 2006, LtCol Gehman was assigned to the VMFAT-101 "Sharpshooters" as an Instructor Pilot, and instructed in Transition and Air-to-Ground Phases. LtCol Gehman served as a Schedules Officer, the Aviation Safety Officer and the Assistant Standardization Officer. In May 2009, LtCol Gehman left active duty, but remained with VMFAT-101 as part of the Marine Corp Reserve Instructor Pilot program and served as the Reserve Squadron Augmentation Unit Operations Representative. During this time, LtCol Gehman attended non-resident Command and Staff College at Marine Corps Recruit Depot, San Diego.
LtCol Gehman began transition training for the MV-22 in May 2012. He completed the transition in August 2012 and was assigned to HMM-764. After the squadron was redesignated VMM-764 in January 2013, LtCol
Gehman became the Reserve Operations Officer. In April 2015, LtCol took command of Marine Medium Tiltrotor Squadron 764. Since then, the squadron has supported the Marine Aircraft Group 41 Battle Staff ACE Integration Training Exercise, two Integrated Training Exercises, and UNITAS Amphibious 2015 in Rio de Janeiro, Brazil.