Basic assumptions when housing soldiers in accommodation units (9)

I believe the answer is:

tenements

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'accommodation units' is the definition.

I don't understand the rest of the clue.

(Other definitions for tenements that I've seen before include "Run-down buildings housing several families" , "Large houses with a large number of families" , "Large run-down buildings found in slums" , "Blocks of flats (US)" , "Buildings rented for living in, as in city slums" .)

I've seen this clue in The Telegraph.

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