This might also be because it’s less glamourous. U-Boat captains and the navy officers are a bit lower on the cool ladder than spies or American presidents when it comes to copying their style it would seem. The Crombie for instance has a pedigree among the Great and the Good that is semi-legendary and that's before we even get started with its Skinhead history.
But the Peacoat is still a solid choice. It has the advantage of being shorter and more everyday than the Crombie. It's usually heavier than your Harringtons, made generally of heavy wool (in either navy or dark grey) with distinctive broad lapels and a double-breasted front. The buttons traditionally have an anchor on them or a similar continuation of the naval theme. They can also accomodate your paisley scarf in the V-neck or you can button up to the top. What's not to like?
Oddly enough, despite being much older than other more "Mod" coats it has changed relatively little in its 200-year history. A few vintage versions still kick around, but if you want something a bit sharper than the Parka, but less formal than the full length overcoat, I’d invest in a Peacoat from a mainstream high street store.
Funnily enough you'll find they’re better quality, slimmer fitting and actually better looking.