Not the first way of working with navy school (9,6)
I believe the answer is:
secondary modern
'school' is the definition.
(secondary modern school is a kind of school)
'not the first way of working with navy' is the wordplay.
I cannot quite see how this works, but
'not' could be 'con' (I've seen this in other clues) and 'con' is found in the answer.
'first' could be 'a' (first letter of the alphabet) and 'a' is found in the answer.
'way' could be 'mode' (synonyms) and 'mode' is found within the answer.
'navy' could be 'rn' (abbreviation for Royal Navy) and 'rn' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for secondary modern that I've seen is " Old school".)