The Storm Fortress

The Storm Fortress was a virtual representation of one of Shay Cormac's genetic memories stored in the Helix, relived by a research analyst through the Animus.

Description
Shay and Gist sailed with the Royal Navy to sink the Assassins' most dangerous ship, the Storm Fortress.

Dialogue
As British gunboats neared the Storm Fortress in the midst of a storm, they were destroyed by its carronades. Upon being damaged severely, the Storm Fortress was joined by two other Men O' War, the Argonaut and the Sceptre. The Morrigan was able to sink the Storm Fortress, as well as the Argonaut and the Sceptre.
 * Gist: There she is, captain! The Storm Fortress!
 * Shay: The rumors did not embellish the truth. She's a leviathan.
 * Gist: She's firing mortars, captain!
 * Shay: We must get closer to the beast if we're to bring her down!
 * Gist: We should avoid her broadsides, captain! She's much too powerful there!
 * Gist: Dear god! We'll be overrun!
 * Shay: We've beaten the odds before, Gist. We shall do so again.
 * Gist: Fighting in this storm is madness! I can't distinguish friend from foe!
 * Shay: Neither can they. With any luck they'll obliterate one another.

Outcome
Shay sank the Storm Fortress and her escorts, thus maintaining the British hold on the Arctic seas.

Reference

 * Assassin's Creed: Rogue