As Commander of USMARCENT, Neller oversaw "the worst loss of U.S. airpower in a single incident since the Vietnam War" Neller's assignments in the operating forces include: Rifle and Weapons Platoon Commander and Company Commander with Company L, 3rd Battalion, 4th Marines, 3rd Marine Division; Commanding Officer, Company A, 1st Battalion, 1st Marines; Commanding Officer, 3rd Light Armored Infantry Battalion (LAI) and Commanding Officer, 6th Marine Regiment from 10 July 1998 to 6 July 2000. While with 3rd LAI he participated in Operation Restore Hope in Somalia. As the Commanding Officer, Marine Corps Security Force Company, Panama, he participated in Operations Just Cause and Promote Liberty. Additionally, he served as Executive Officer, 7th Marine Regiment, G-3, II Marine Expeditionary Force and G-3, 2nd Marine Division.