Beam ruins lost below the ocean (9)

I believe the answer is:

submarine

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

'below the ocean' is the definition.
I can't judge whether this defines the answer.

'beam ruins lost' is the wordplay.
'lost' is an anagram indicator.
'beam'+'ruins'='beamruins'
'beamruins' is an anagram of 'SUBMARINE'.

Can you help me to learn more?

(Other definitions for submarine that I've seen before include "Under the sea" , "Submersible warship" , "... underwater craft" , "Under the surface" , "snack" .)

I've seen this clue in the Sydney Morning Herald.

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