Engineers having behaved and responded (7)
I believe the answer is:
reacted
'responded' is the definition.
('react' can be a synonym of 'respond')
'engineers having behaved' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'having' says to put letters next to each other.
'behaved' becomes 'acted' (acting is a kind of behaving).
're'+'acted'='REACTED'
'and' is the link.
(Other definitions for reacted that I've seen before include "Responded to a stimulus" , "Showed a response" .)