It's about wrecking a vessel (1-4)

I believe the answer is:

u-boat

I'm a little stuck... Click here to teach me more about this clue!

'vessel' is the definition.
(I've seen this before)

'it's about wrecking a' is the wordplay.
'about' can be anagrammed to 'U-BOAT'.
But, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for u-boat that I've seen before include "Submersible warship of WWII" , "Sea vessel" , "Take pool exercise" , "Submersible warship armed with torpedoes" , "German submarine of WW2" .)

I've seen this clue in the Evening Standard.

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