Ancient oared vessel heard by military engineers (6)
I believe the answer is:
bireme
'ancient oared vessel' is the definition.
'bireme' can be an answer for 'vessel' (I have seen 'Ancient vessel' mean 'bireme' so perhaps 'vessel' could also mean 'bireme'). I am unsure of the 'ancient oared' bit.
'heard by military engineers' is the wordplay.
'heard by' becomes 'bi' (I can't justify this - if you can you should believe this answer much more).
'military engineers' becomes 'REME' (Royal Electrical and Mechanical Engineers).
'bi'+'reme'='BIREME'
Can you help me to learn more?
(Other definitions for bireme that I've seen before include "old vessel?" , "with two tiers" , "rowing boat" , "Ancient vessel" , "Ancient oared warship" .)