I don't know if people thinks in early small coastal subs, adaptable U VII large U IX that predated us coastal shipping or late model Walther subs.
But...why U boote ? Ask japanese merchantmen and IJN crewmembers their opinion about USN subs, the silent service. Of course the german subs obtained well deserved fame, but from May 43 onwards they were completely outdated. The US Silent Service grew to finish the war as the masters of the deep.
So we may call the "Gato"...