Servicemen who have a job to do (4,5)
I believe the answer is:
'servicemen who' is the definition.
The definition and answer can be both groups as well as being singular nouns.
Maybe there's a link between them I don't understand?
'a job to do' is the wordplay.
'a job' becomes 'task' (synonyms).
'to do' becomes 'force' (forcing is a kind of doing).
'have' is the link.
Can you help me to learn more?
(Other definitions for task force that I've seen before include "Group organised for a specific purpose" , "Single-purpose group" , "working group" , "Special work group" , "subcommittee" .)