I'm still chugging along with semi vanilla (I made my own mods) 1.4, haven't gotten around to 1.5 yet so no gots Das Boot. I have seen and avoided attacking Dutch, Australian, New Zealand, and US ships in Asiatic careers. However, never saw Spain, France, Switzerland and Norway flags in the Pacific. Spain and Switzerland were pro-Nazi neutrals, France and Norway were both occupied, and does Switzerland even have a Navy or merchant marine? Last I checked it was landlocked with no sea ports.
Ship models are all the same except for the Liberty cargo, pretty much Japanese "small old engine aft" or "large old split freighter" or whatever with a different flag. Playing with manual targeting OR no map contacts there's a quick way to check IFF, but playing with manual targeting AND no map contacts you gotta double check the flag before firing. With improved environments heavier fog that gets downright hairy, the flag is a gray blur until I'm too close for the fish to arm.