Room in ready-made fighting machine (3,4)

I believe the answer is:

red army

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'fighting machine' is the definition.
The definition suggests a singular noun which matches the answer.

'room in ready-made' is the wordplay.
'room' becomes 'rm' (abbreviation).
'in' indicates putting letters inside.
'made' indicates anagramming the letters.
'ready' with letters rearranged gives 'reday'.
'rm' going into 'reday' is 'RED ARMY'.

Can you help me to learn more?

(Other definitions for red army that I've seen before include "Soviet troops" , "Cold War divisions?" , "Left soldiers" , "Revolutionary fighters" , "Leon's offensive baby" .)

I've seen this clue in the Sydney Morning Herald.

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