Abs out to sink German subs (1-5)

I believe the answer is:

u-boats

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

'german subs' is the definition.
(I've seen this in another clue)

'abs out to sink' is the wordplay.
'abs out' can be anagrammed to 'U-BOATS'.
Though, I'm unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for u-boats that I've seen before include "German subs" , "Submersible ships of WW2" , "German submarines of second World War" , "Submersible warships" , "German submarines in WW2" .)

I've seen this clue in The Irish Independent.

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.