Harrison later led 12th Defense battalion during the Battle of Cape Gloucester at New Guinea at the end of December 1944 until he was replaced by Merlyn D. Holmes and appointed commanding officer of 11th Marine Artillery Regiment within 1st Marine Division under Major General William H. Rupertus. His regiment was designated artillery group for the Peleliu Operation in September 1944 and even with a minimum of motor transportation available, Harrison coordinated artillery shelling on well entrenched enemy forces. His actions destroyed a large number of Japanese units, and this helped to win the campaign. For his actions and leadership during the battle, Harrison received the Legion of Merit with Combat "V" and also the Navy Presidential Unit Citation.