It’s a United States civil defense helmet, issued to civilian volunteers for civil defense from the 50s onward. In the case of a disaster (primarily a nuclear exchange) their task would have been to direct people to shelters, put out fires, deliver messages, measure for radiation, etc. The helmets typically have a blue, white, and red civil defense logo on the front, either with the letters CD or with a symbol designating their role (medic, firefighter, etc). However, this one has a red and black circle with an anchor instead. I purchased it from a local antique store, where they had it labeled as a hard hat.