German submarine in World Wars I and II (1,4)

I believe the answer is:

u boat

(Other definitions for u boat that I've seen before include "hidden destroyer" , "submarine" , "sub" , "threat to wartime shipping" , "Killer" .)

I've seen this clue in The Mirror.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.