Navy Warhead
Lv45-50 War Frigate
EITC Warhead
Lv45-50 War Frigate
Use Firebrand as the Broadsides and Explosives as the upper deck guns.
These two ships usually appear together. They don't really carry good cargo in terms of treasure, but they do carry Loot Skull Chests that hold powerful weapons. They can also do a lot of damage in an attempt to protect the weapons.
Navy Nightwatch
Lv15-20 Frigate
Uses Firebrand as the Broadsides and Roundshot as the upper deck guns.
These ships do a ton of damage - even for their level - but because of the ton ( Literally ) of power, they aren't too fast, and can't take too many hits, so they're easy to sink.