The soldiers' joint, afloat? (9)

I believe the answer is:

troopship

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

'the soldiers' joint afloat?' is the definition.
I can't tell whether this definition defines the answer.

'the soldiers' joint' is the wordplay.
'the soldiers'' becomes 'troops' (groups of soldiers).
'joint' becomes 'hip joint' (part of body).
'troops'+'hip'='TROOPSHIP'

Can you help me to learn more?

(Other definitions for troopship that I've seen before include "boat" , "As carrier" , "Military transport vessel" , "Army vessel" .)

I've seen this clue in the Evening Standard.

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