Swim around soldiers, say? (7)
I believe the answer is:
breathe
'say?' is the definition.
(thesaurus)
'swim around soldiers' is the wordplay.
'swim' becomes 'bathe' (bathe can mean to swim).
'around' indicates putting letters inside.
'soldiers' becomes 'RE' (Royal Engineers).
'bathe' placed around 're' is 'BREATHE'.
(Other definitions for breathe that I've seen before include "eg Inhale" , "Take inspiration" , "Do this before you go under" , "Inspire and expire air" , "Expel gas" .)