American navy in Naples moved north (13)
I believe the answer is:
Here is my best explanation:
'american' is the definition.
(Pennsylvanian is an example)
'navy in naples moved north' is the subsidiary indication.
'moved' is an anagram indicator.
'north' becomes 'n' ('N' can be a synonym of 'north').
'navyinnaples' anagrammed gives 'pennsylvania'.