noun
steel helmet
Refers to a military-style steel helmet, such as those used in wartime.
兵士たちは鉄兜をかぶって塹壕にいた。
The soldiers were in the trench wearing steel helmets.
General term for any protective helmet, including sports and construction helmets. 鉄兜 specifically refers to a steel military helmet.
Compound of 鉄 (てつ, 'iron, steel') and 兜 (かぶと, 'helmet').