Officers in naval vessel change directions (10)

I believe the answer is:

subalterns

'officers' is the definition.
(subaltern is a kind of officer)

'naval vessel change directions' is the wordplay.
'naval vessel' becomes 'sub'.
'change' becomes 'alter' (altering is a kind of changing).
'directions' becomes 'ns' (N is an example).
'sub'+'alter'+'ns'='SUBALTERNS'

'in' acts as a link.

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