Demand by engineers for salvage (7)
I believe the answer is:
reclaim
'salvage' is the definition.
(thesaurus)
'demand by engineers' is the wordplay.
'demand' becomes 'claim' (claiming is a kind of demanding**).
'by' says to put letters next to each other.
'engineers' becomes 're' (Royal Engineers).
'claim' after 're' is 'RECLAIM'.
'for' is the link.
(Other definitions for reclaim that I've seen before include "recovery like this" , "Win back" , "Make (land) available for use" , "From sea, rescue" , "Salvage" .)