One-time destroyer of destroyers? (1-4)
I believe the answer is:
u-boat
'destroyer of destroyers?' is the definition.
'u boat' can be an answer for 'destroyer' (I have seen 'hidden destroyer' mean 'u boat' so perhaps 'destroyer' could also mean 'u boat'). I am not certain of the 'of destroyers?' bit.
'one-time' is the wordplay.
I cannot really understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'time' could be 't' (abbreviation) and 't' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for u-boat that I've seen before include "Take pool exercise" , "German submarine of WW2" , "Submersible warship of WWII" , "German wartime submarine" , "German WW 2 sub" .)