This is likely a German Stahlhelm, which became standard-issue in the later years of World War I. These steel helmets were first introduced in 1916 as a replacement for the iconic leather Pickelhaube helmets, which had proved to be ineffective and impractical on the battlefield. The Stahlhelm almost completely enveloped the wearer's head with durable steel. Its design was usually effective against the constant threat of shrapnel and succeeded in dramatically reducing head-related battlefield casualties.
