Impregnable base in USA, all newly set out (12)

I believe the answer is:

unassailable

'impregnable' is the definition.
(I know that impregnable can be written as unassailable)

'base in usa all newly set out' is the wordplay.
'newly set out' is an anagram indicator.
'base'+'in'+'usa'+'all'='baseinusaall'
'baseinusaall' with letters rearranged gives 'UNASSAILABLE'.

(Another definition for unassailable that I've seen is " Unable to be attacked".)

I've seen this clue in The Times.

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