Cover of navies oddly involved in European run (8)
I believe the answer is:
envelope
'cover' is the definition.
(I know that envelope is a type of cover)
'navies oddly involved in european run' is the wordplay.
'oddly' indicates alternate letters (letters in odd-numbered positions).
'involved in' indicates putting letters inside.
'european' becomes 'e' (abbreviation e.g. EU).
'run' becomes 'lope' (lope is a kind of run).
The alternating letters of 'navies' are 'nve'.
'e'+'lope'='elope'
'nve' inserted within 'elope' is 'ENVELOPE'.
'of' is the link.
(Other definitions for envelope that I've seen before include "Wrapper for 31ac" , "something to push?" , "what's to be posted in here?" , "Coat" , "Container for letter" .)