A couple in our navy are obsolete (7)
I believe the answer is:
outworn
'obsolete' is the definition.
(thesaurus)
'a couple in our navy' is the wordplay.
'a couple' becomes 'two' (I've seen this before).
'in' is an insertion indicator.
'navy' becomes 'n' (common abbreviation eg in RN Royal Navy).
'two' inserted into 'our' is 'outwor'.
'outwor'+'n'='OUTWORN'
'are' is the link.
(Other definitions for outworn that I've seen before include "Old, exhausted or no longer used as dress" , "Old-fashioned" , "Obsolete, dated" , "Jaded" , "Out of date" .)