BGen Gallman 's command tours include Commanding Officer of Marine Aircraft Group Twenty-Six (MAG-26) Personnel Support Detachment (PSD) from February of 2012 to June of2013; Marine Tiltrotor Squadron 261 (VMM-261) from June of 2013 to May of 2015, Marine Aviation and Weapons Tactics Squadron One (MAWTS-1) from May of 2018 to November of 2019, and Assistant Wing Commander, 1st Marine Aircraft Wing from July 2023 to May 2025.

His staff assignments include the Senior Military Advisor to the Secretary of the Navy; Deputy Division Chief of the Joint Capabilities Division (JCD), Joint Staff J8; Executive Officer of The Basic School, Training and Education Command; Aviation Plans and Programs Three (APP-3) Branch Head, Headquarters Marine Corps Aviation; Type/ Model/ Series Transition Officer, 3d Marine Aircraft Wing; Operations Officer, Marine Medium Helicopter Squadron 166 (HMM-166); Marine Aviation Weapons and Tactics Volume Manager, 561st Joint Tactics Squadron, Nellis Air Force Base; Weapons and Tactics Instructor, Marine Aviation Weapons and Tactics Squadron 1; and various squadron billets in operations, aviation maintenance and pilot training.

BGen Gallman graduated from Tuskegee University, Tuskegee, AL. with a BS in Aerospace Engineering in 1992. He graduated Basic Officer Course (BOC) at The Basic School in 1995. BGen Gallman has earned a master's degree in National Security and Strategic Studies from the Naval War College in 2007, graduated from the National War College with a Master's in National Security Strategy in 2015 and completed the Harvard Business School Advanced Management Program in 2017.