Survive, being first to follow U-boats? (7)
I believe the answer is:
subsist
'survive' is the definition.
(synonyms)
'first to follow u-boats?' is the wordplay.
'first to' becomes 'ist' (I've seen this in other clues).
'follow' means one lot of letters go next to another.
'u-boats?' becomes 'subs' ('sub' can be a synonym of 'u-boat').
'ist' put after 'subs' is 'SUBSIST'.
'being' is the link.
(Other definitions for subsist that I've seen before include "Survive at minimal level" , "Have the necessities for life" , "Live at a minimal level" , "keep going" , "Eke out a living" .)