Save engineers given second signal (6)
I believe the answer is:
rescue
'save' is the definition.
(rescuing is a kind of saving)
'engineers given second signal' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'given' is a charade indicator (letters next to each other).
'second' becomes 's' (common abbreviation).
'signal' becomes 'cue' (I've seen this before**).
're'+'s'+'cue'='RESCUE'
(Other definitions for rescue that I've seen before include "Extricate" , "Secure (anag) - release" , "Save someone from a dangerous situation" , "Deliver from danger" , "Free someone from trouble" .)