Professor Donnellan served for 30 years as a Marine Corps officer with command assignments at the platoon, company, infantry battalion and training installation level. His assignments as a Colonel included Command of the Marine Corps Mountain Warfare Training Center and service at combatant command and service component levels. He commanded 2nd Battalion, 3rd Marines on combat deployments to both Afghanistan and Iraq. Prior to joining Joint Military Operations, Professor Donnellan was a member of the faculty in the College of Maritime Operational Warfare, where he taught the Maritime Staff Operators Course.