There's a fair bit of info about the history on the web, even a suggestion that the real original design was Italian. I wouldn't dismiss that out of hand. Anyway, it was so good that the US defence industry tried to improve it, and apparently couldn't. Or, at least, it was a "we want them now" situation. I think the main military divergence was the plastic can for water, which did have a screw cap. It wouldn't astonish me if there were a screw-cap fuel can as well, but I've never seen one. I think I've said it before, but the jerrycan is such a ubiquitous item that's it's worth getting right. And "right" isn't down to having a lot of polygons.