Early forerunner of the famous Stahlhelm. It consisted of a leather cap with a 6 mm steel plate mounted on its front. It was mainly used by the Sturm-Battallion Nr. 5 (Rohr), famous for its shock-troop-tactics. Pictures of one can be found here: https://www.iwm.org.uk/collections/item/object/30100057
gaede-helmet