Audible attempt by military engineers to identify ancient warship (7)
I believe the answer is:
trireme
'ancient warship' is the definition.
(I've seen this in another clue)
'audible attempt by military engineers' is the wordplay.
'audible' indicates a 'sounds like' (homophone) clue.
'attempt' becomes 'try' (synonyms).
'by' says to put letters next to each other.
'military engineers' becomes 'REME' (Royal Electrical and Mechanical Engineers).
'try' is a homophone of 'tri'.
'tri'+'reme'='TRIREME'
'to identify' is the link.
(Other definitions for trireme that I've seen before include "Ancient rowed ship" , "Roman/Greek galley" , "Ancient warship with three banks of oars" , "Ancient Greek or Roman war galley" , "Ancient galley with three tiers of oars on each side" .)