1/5 made its most notable contribution at the Battle of Belleau Wood on 6 June 1918, when it conducted the first offensive actions of the battle in seizing Hill 142. The battalion, at first with only two companies due to the other companies not being relieved in time, assaulted the open wheat fields of the hill with bayonets fixed under the fire of German machine gun and artillery fire. In a battle that claimed 325 1/5 lives, Gunnery Sergeant Ernest A. Janson became the first Marine to earn the Medal of Honor in World War I. From December 1918 to July 1919, the battalion participated in the occupation of the German Rhineland. It then re-deployed to Marine Corps Base Quantico, Virginia and de-activated in August 1919.