Officer needing loo in speech in US, that would be left here (5,10)

I believe the answer is:

first lieutenant

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'officer needing loo in speech in us that would be left here' is the definition.
'first lieutenant' can be an answer for 'officer' (first lieutenant is a kind of officer). I'm unsure of the remainder of the definition.

'officer needing loo in speech in us' is the wordplay.
'officer' becomes 'lieutenant' (lieutenant is a kind of officer).
'needing' is a charade indicator (letters next to each other).
'loo in speech in us' becomes 'first' (I can't justify this - if you can you should give a lot more credence to this answer).
'lieutenant' put after 'first' is 'FIRST LIEUTENANT'.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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