First, not all ships [pleasure craft] have/use AIS.
Also, not all areas are covered. example: Altho listed, with a Cape Cod site, it hasn't shared data in approx 2 mo's
yet a new Rhode Island site has appeared and Boston has good coverage but nothing listed for an actual Site until Portland Maine.
What you will find is many of the Larger Cargo/Tanker/Cruise Ships
and a the Larger Yachts.
As for Military, I have found they are used ONLY when approaching Port [CG Interop / Port Control] and then many are Unlisted on AIS or use Odd Names. You might find a few in the Foreign Ports, but few are listed in US ports once they reach Dock
I was trying to find some of my old Navy ships. They weren't listed.