Fruit, bacon, unlimited by Royal Navy (5)
I believe the answer is:
acorn
'fruit' is the definition.
(acorn is a kind of fruit)
'bacon unlimited by royal navy' is the wordplay.
'unlimited' indicates the central letters (discard the edges or 'limits' of the word).
'by' means one lot of letters go next to another.
'royal navy' becomes 'rn'.
The centre of 'bacon' is 'aco'.
'aco'+'rn'='ACORN'
(Other definitions for acorn that I've seen before include "Source of a great oak" , "From which a tall tree may grow" , "Oak seed" , "Might source" , "Potentially future tree" .)