Win over duke is supported by half of fleet (6)

I believe the answer is:

disarm

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'win over' is the definition.
(I've seen this before)

'duke is supported by half of fleet' is the wordplay.
'duke' becomes 'd'.
'supported by half of fleet' becomes 'arm' (I can't justify this - if you can you should give a lot more credence to this answer).
'd'+'is'+'arm'='DISARM'

Can you help me to learn more?

(Other definitions for disarm that I've seen before include "Render defenceless" , "Placate" , "Remove suspicion" , "to allay hostility" , "Render harmless" .)

I've seen this clue in The Telegraph.

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