That's it! Thank you, Rick! I knew it was on some other naval item other than a weapon. That was driving me crazy! Specifically, it was where the inspiration for this badge was taken, reflected in these designs for dolphins taken from antiquity such as this Roman statue of Neptune. They really look more like koi to me!
(Edit). Just found this which explains the appearance of these dolphins of yore.
https://rwalck.wordpress.com/2015/12...sance-dolphin/