Tonnage of the mother ship? (4)

I believe the answer is:

mass

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'tonnage of the mother ship?' is the definition.
'mass' can be an answer for 'ship?' (thesaurus). I'm unsure of the 'tonnage of the mother' bit.

'mother ship?' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'ship?' becomes 'ss'.
'ma'+'ss'='MASS'

Can you help me to learn more?

(Other definitions for mass that I've seen before include "seasonal midnight service?" , "Lump of material" , "13 [BULK]" , "Catholic church service" , "Church service - collection" .)

I've seen this clue in the Evening Standard.

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