Marines trial exercises in transport hubs (3,9)

I believe the answer is:

air terminals

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'transport hubs' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe you can see an association between them that I can't see?

'marines trial exercises' is the wordplay.
'exercises' is an anagram indicator (letters exercise or move around).
'marines'+'trial'='marinestrial'
'marinestrial' with letters rearranged gives 'AIR TERMINALS'.

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.

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