Undersea menace could be about (1-4)

I believe the answer is:

u-boat

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'undersea menace' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'could be about' is the wordplay.
'could be' indicates an anagram.
'about' is an anagram of 'U-BOAT'.

Can you help me to learn more?

(Other definitions for u-boat that I've seen before include "Sea vessel" , "German World War One or World War Two submarine" , "Submersible warship of WWII" , "Take pool exercise" , "Submersible warship armed with torpedoes" .)

I've seen this clue in The Telegraph and The Sun.

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