Kind of vessel apt to sink a lot (5)

I believe the answer is:

uboat

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'apt to sink a lot' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'kind of vessel' is the wordplay.
'kind of' becomes 'u' (I can't justify this - if you can you should give a lot more credence to this answer).
'vessel' becomes 'boat' (boat is a kind of vessel).
'u'+'boat'='UBOAT'

Can you help me to learn more?

(Other definitions for uboat that I've seen before include "Vessel" , "What convoy tried to avoid" , "Sub" , "Warship" .)

I've seen this clue in the Evening Standard.

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