Eagle sailors found in middle of Greece (4)
I believe the answer is:
erne
'eagle' is the definition.
(erne is a kind of eagle)
'sailors found in middle of greece' is the wordplay.
'sailors' becomes 'rn' (abbreviation for Royal Navy).
'found in' indicates putting letters inside.
'middle of' says to take the centre.
The middle of 'greece' is 'ee'.
'rn' put into 'ee' is 'ERNE'.
(Other definitions for erne that I've seen before include "Eagle, river and lough" , "Sea-eagle in an Irish lake" , "Marine flyer" , "Great lake in Fermanagh with lots of islands" , "Fish-eating sea eagle" .)