Money set aside to finance submarine warfare? (7,4)

I believe the answer is:

sinking fund

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'money' is the definition.
(sinking fund is a kind of money)

'set aside to finance submarine warfare?' is the wordplay.
I cannot really understand how this works, but
'set' could be 'sink' (to go lower) and 'sink' is present in the answer.
'finance' could be 'fund' (funding is a kind of financing) and 'fund' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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