Plane that sounds like a submarine perhaps? (8)
I believe the answer is:
sandwich
'submarine perhaps?' is the definition.
(submarine is a kind of sandwich)
'plane that sounds like a' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sandwich that I've seen before include "Quick snack" , "Two slices with something in between" , "Maybe double-decker" , "Golf course - snack" , "One of the Cinque Ports" .)