Marine helmets are part of the Marine armor set in game. It covers the eyes, ears, nose and jaw (as opposed to just the head as the other helmets) and it also provides protection against burns.
It can be crafted with 40 plasteel and 1 advanced component or found on incoming pirates.
It is the most expensive helmets and comparable to a plasteel advanced helmet which requires 75 plasteel and 2 components to craft. While the marine helmet has better protection, the plasteel advanced helmet has higher HP and thus lasts longer.
In 0.19/1.0 it received a recipe change and a rename.