— Dunn to Recker in Baku
Staff Sergeant William Dunn was a US Marine in the US military and former leader of Tombstone. After being wounded in action and having his right leg amputated, he was killed after his team was involved in a car crash that left their vehicle underwater. He ordered Recker to shoot the windshield out and save the other two members of the team, sacrificing himself and drowning in the process.
Dunn, Recker, and Irish had served together long before the events of Battlefield 4, as said by Pac, who had joined Tombstone about a year prior. Dunn also has a wife, as stated in Baku, Shanghai, and South China Sea.
- Main article: Baku
Dunn led Tombstone on the mission in Baku, Azerbaijan to obtain intelligence from a defecting Russian Army general. After the hand-off went "pear-shaped", and the squad tried to make their way to their extraction point, Dunn had been caught under rubble as a result of a recent ambush from a Russian helicopter. Dunn had his leg amputated and was driven away, only to crash into the sea along with his squad. He ordered them to leave him in the vehicle, which they reluctantly agreed to. As the vehicle sank, Dunn died in the Caspian Sea.
- In the "Fishing in Baku" trailer, Dunn wore the Jolly Roger of the famous English pirate Calico Jack Rackam, and equipment used by Navy SEALs, as indicated by the use of the AORI/AORII camouflages and chest rig/vest configuration. Upon the game's release, his model was changed to a generic model used by the US Assault class in Multiplayer, losing the unique equipment and Jolly Roger patch.
- He resembles the main character of the war film Passchendaele (Micheal Dunne) in both appearance and name.
- Dunn wears the standard USMC uniform also worn by Major Greenland and many generic Marines, albeit Dunn having tiger stripe camouflage trousers.
- After Dunn's death in Baku, Recker keeps the MP412 Rex that was given to him by Dunn and carries it by default thereafter. The name of the assignment that unlocks it in multiplayer is identical to Dunn's codename.