Crossword Genius

Watertight chamber is thus enclosed in metal (7)

Ross

I believe the answer is:

caisson

I'm a little stuck... Click here to teach me more about this clue!

'watertight chamber' is the definition.
(I've seen this before)

'is thus enclosed in metal' is the wordplay.
'thus' becomes 'so' ('so' can be a synonym of 'thus').
'enclosed in' is an insertion indicator.
'metal' becomes 'can' (I can't justify this - if you can you should believe this answer much more).
'is'+'so'='isso'
'isso' inserted into 'can' is 'CAISSON'.

Can you help me to learn more?

(Other definitions for caisson that I've seen before include "watertight chamber" , "Structure excluding water from construction" , "Water-excluding case" , "So I scan the ammunition wagon" .)

I've seen this clue in The Independent.
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