One royal nearly made a lot of ships (6)
I believe the answer is:
armada
'lot of ships' is the definition.
'one royal nearly made a' is the wordplay.
'one' becomes 'a'.
'royal' becomes 'r' (abbreviation).
'nearly' means to remove the last letter.
'made' with its final letter taken away is 'mad'.
'a'+'r'+'mad'+'a'='ARMADA'
(Other definitions for armada that I've seen before include "Spanish war fleet" , "Large Spanish fleet" , "Old Spanish fleet" , "Fighting unit" , "Large war fleet" .)