During World War I, Neilson served in the United States Army infantry as a lieutenant. ️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️ 1918 Neilson participated in the Second Battle of the Marne
, during which his commanding officer was killed.<unk>, during which his commanding officer was killed. During the battle he was wounded, but still took command of his fellow soldiers and safely entrenched them for 24 hours.<unk> During the battle he was wounded, but still took command of his fellow soldiers and safely entrenched them for 24 hours. He suffered a bullet wound to the stomach and several shrapnel wounds.<unk> He suffered a bullet wound to the stomach and several shrapnel wounds. ️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>