- "We were definitely going for some Dead Space moments."
- — Glen Schofield
Call of Duty: Vietnam (internally titled Fog of War) is a cancelled installment of the Call of Duty series that was under development by Sledgehammer Games. It was stated to be taking place in the 1960s and 1970s, in Cambodia, Vietnam and Laos.
The game was planned to be in the action/adventure genre and would've been the first third-person only Call of Duty game. After eight months of development, the game had up to 15 minutes playable, at which point Activision offered Sledgehammer the opportunity to help Infinity Ward in the development of Call of Duty: Modern Warfare 3.
In January 2011, it was confirmed the action-adventure game would be cancelled, or simply put on hold. Glen Schofield referred to the game as "most likely cancelled" when interviewed in October 2011.
Sledgehammer went on to develop Call of Duty: Advanced Warfare, confirming the game's cancellation. During an interview with Glen Schofield in May 2014, he revealed more information on the cancelled project and what the studio had been working on.
In an interview with Gameinformer, Glen Schofield stated that if the studio was ever asked to make a third-person Call of Duty game again, they would continue development on Call of Duty: Vietnam. 
- Fritz, Ben."Activision calls in reinforcements for next Call of Duty game", latimes.com, 20 January 2011.
- Reilly, Jim."Call of Duty Action Title Likely Cancelled", gameinformer.com, 17 October 2011.
- Campbell, Evan."Sledgehammer Developed a Third-Person Vietnam War Call of Duty Demo", ign.com, 5 May 2014.
- Dumitrescu, Andrei."Sledgehammer Games: Canceled Call of Duty Vietnam Game Could Be Revived", softpedia.com, 15 May 2014.