Not in good condition in a submarine operation (5,3,7)
I believe the answer is:
under the weather
'a submarine operation' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'not in good condition' is the wordplay.
I cannot really understand how this works, but
'not' could be 'un' (I've seen this in other clues) and 'un' is found within the answer.
'condition' could be 'weather' (weather is a kind of condition) and 'weather' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for under the weather that I've seen before include "Depressed" , "with clouds gathering overhead" , "not so good" , "the worse for wear" , "where you have to look for this crossword?" .)