Karma

The Karma or fish crest Helmet was the traditional númenorean Helmet worn by members of the guild of venturers.It was basically a high steel-helmet with a huge fish-crest, cheek guards and nasals covered by multi-colored leather.

Derivations of the original numenorean model were worn by black númenoreans and the early corsairs of umbar until roughly the late third age.

speculations
Tolkien´s sketch of the Karma may have been inspired by the historical burgonet helmet.