US navy cornered bogus mapmakers (8,6)

I believe the answer is:

ordnance survey

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

'bogus mapmakers' is the definition.
I can't judge whether this definition defines the answer.

'us navy cornered' is the wordplay.
'us navy cornered' anagrams to 'ORDNANCE SURVEY'.
Though, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for ordnance survey that I've seen before include "UK map-makers" , "Charters" , "Geography department" , "UK map makers" .)

I've seen this clue in The Daily Mail.

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