Use artillery for cover (5)

I believe the answer is:

shell

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'cover' is the definition.
(shell is a kind of cover)

I can't explain the rest of the clue.

(Other definitions for shell that I've seen before include "layer of jacket" , "bomb?" , "Tortoise's home" , "Crustacean's protection" , "Hull" .)

I've seen this clue in The Telegraph.

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