It's simple to deploy army under it (11)

I believe the answer is:

rudimentary

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'it's simple' is the definition.
I can't tell whether this definition defines the answer.

'deploy army under it' is the wordplay.
'deploy' is an anagram indicator (I've seen 'deploying' mean this).
'army'+'under'+'it'='armyunderit'
'armyunderit' anagrammed gives 'RUDIMENTARY'.

'to' is the link.

Can you help me to learn more?

(Other definitions for rudimentary that I've seen before include "Undeveloped" , "Primitive" , "Limited to basics" , "Immature" , "Basic" .)

I've seen this clue in The Guardian.

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