Warship seen from coast, heading for Rosyth (7)
I believe the answer is:
cruiser
'warship' is the definition.
(I know that cruiser is a type of warship)
'coast heading for rosyth' is the wordplay.
'coast' becomes 'cruise' (I've seen this before).
'heading for' suggests taking the first letters.
The initial letter of 'rosyth' is 'r'.
'cruise'+'r'='CRUISER'
'seen from' acts as a link.
(Other definitions for cruiser that I've seen before include "Leisure yacht; warship" , "A fast warship, sounds leisurely" , "Old warship" , "Relatively fast warship" , "privateer" .)