Sir James Gunn's Sword

Sir James Gunn's Sword was a broadsword obtainable by Shay Cormac during the 18th century. Having once belonged to the famous Scottish Templar Knight James Gunn, it was stored alongside his armor in a warehouse in Fort de Sable some time after his death. Shay acquired it at an unknown point during his time in the North Atlantic after collecting all the Templar crosses necessary to unlock the warehouse door.

Reference

 * Assassin's Creed: Rogue – The Siege of Fort de Sable