The Royal Sovereign was one of five legendary ships, encountered by the pirate Edward Kenway in the Caribbean, during the 18th century. She was the sister ship of HMS Fearless; both were identical, save for the reversed coloring of their sails and hull. They could be found sailing beyond the Bahamas, on the edge of the Atlantic Ocean.
The pair became notorious for sailing in tandem and for their tactics in naval warfare. They could flank an enemy ship, surrounding her from both sides, and firing upon her with devastating power. If either Fearless or the Royal Sovereign was sunk, the other one would set herself alight and use her maneuverability to viciously ram the opposing ship. Despite their tandem battle strategies and impressive firepower, both ships were eventually sunk by Kenway's Jackdaw.
- Historically the Royal Sovereign underwent a 'Great Repair' from 1722 to 1725, probably referencing her battle with the Jackdaw. She remained in service with the Royal Navy until 1768 when she was broken up.
- In real life, the ship is mainly called the HMS Royal Sovereign like every other Royal Navy ship where it should have been called but in the game, it was just called the Royal Sovereign.