Army a long time producing prisoners (8)
I believe the answer is:
hostages
'prisoners' is the definition.
(hostage is a kind of prisoner)
'army a long time' is the wordplay.
'army' becomes 'host' (host is a kind of army).
'a long time' becomes 'ages' (I've seen this before).
'host'+'ages'='HOSTAGES'
'producing' is the link.
(Other definitions for hostages that I've seen before include "People detained" , "Victims of kidnap" , "They're held as sureties against demands" , "Prisoners held as sureties" .)