Part of my Weekly Tolkien Sketchblog
Several attempts at the Numenorean "Karma," a type of seafarer's helmet referenced only once in Tolkien's entire legendarium, as an explanation for this rather bizarre looking drawing of his, which appeared on the original cover of Unifinished Tales [link]
(you've gotta love Tolkien for stuff like this; just when all the Bayeux tapestry-style long mail shirts and conical iron caps are in danger of getting monotonous, he'll throw a big psychedelic snail-looking thingie in the mix, just to shake things up)
trying to find some historical influences which felt fitting for a more realistic version of tolkien's illustration, I ended up drawing primarily from the classical greek corinthian, the macedonian helmets of alexander's armies, and the renaissance era burgonets, with a healthy dose of the good old roman/gallic helmets, among others. It seems appropriate, for illustrating the numenoreans, to draw (in addition to armor sources from antiquity) from a later, more advanced period in the history armor making than is generally seen in the other cultures of middle earth. despite their hubris (which ofcourse lead to their downfall) the numenoreans were indeed a superior people. I really liked the idea that that bulbous, octopus-like bulge in the back (especially on the archaic model, when worn back on the head like a greek hoplite) would give the wearer this elongated, alien like silhouette which, combined with the great stature of the dunedain (in their hey day they're supposed to have averaged at about seven feet) and their might and splendor, would indeed give the comparatively primitive men of middle earth the impression of alien, even godlike beings (basically the Middle-Earth explanation for those prometheus-esq pop science theories about tall alien (or, often enough and fittingly, Atlantean) teachers coming to earth in the ancient past; one could imagine rough, mythologized likenesses of numenoreans painted by primitives onto cave walls, or carved on standing stones)
I don't think of the Karma as one specific type of helmet per se, but rather, like real historical helmet designs such as the basinet or spangenhelm, as a particular (and evolving) 'school' of helmet construction, consisting of many different designs but charactorized by a few consistent features, nor was it by any means the only style of helmet made in Numenor. I think of them as having been a phenomenally rich culture aesthetically, much of which was lost forever in the drowning, and of the majesty of which only a small part (and perhaps not even the better part) survived and continued in the realms of Gondor and Arnor.