Fighting weight of H.M.S. Belfast? (7)

I believe the answer is:

cruiser

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'fighting weight' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for cruiser that I've seen before include "Warship; leisure craft" , "Speedy warship" , "Warship - pleasure boat - boxing weight" , "Large warship" , "A fast warship, sounds leisurely" .)

I've seen this clue in the Evening Standard.

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