We know that the end of the year will mark a new Call of Duty

World at War II

A scene from one of the told stories.

Literal fuel to the fire.

Black Ops 1.5

Is this a conflict the CoD games want to return to?

Welcome back to the jungle?

Black Ops 2.5

Not pictured: a change of pace.

The dressage event, for one, was a real surprise.

Black Ops III

"Look at me! This is important! Do I have any poppy seeds in my teeth? I just ate a muffin."

Why is the future always on fire?

Zombies

Nothing but zombies? Hmm.

Rest assured there'll be more of this one way or another.

Treyarch titles tend to involve a comparatively longer solo experience, an extensive cooperative mode and addictive multiplayer. With no official word yet on what’s coming from Treyarch at the end of 2015, let’s take a closer look at some of the options that are possible…A few years ago, the prospect of the Call of Duty franchise shifting back to its World War II roots was a laughable concept, what with the futuristic forward thrust of the series. That was until Black Ops II took the fight to 2025 and most-recent entry Advanced Warfare exo-jumped into the year 2054. This means the future of Call of Duty has to push even further into the 21st century (or beyond), or it has to get at least one of the three developers to shuffle back in time.Treyarch was the team burdened with the reality of creating a World War II-themed title after the mega-success of Modern Warfare. When the gaming world was going bananas over a contemporary weapons locker, Treyarch was thrown into the hurt locker by dragging CoD fans back to the familiar ancient arsenal of the Second World War. What better team to boldly take the franchise back to World War II - an era that’s now all but neglected in the gaming space , despite its popularity at the time of the release of World at War - and show that there are stories to be told in the last Great War.This prospect has already been potentially teased on the Treyarch Facebook page with an image relating to the attack on Pearl Harbor alongside the quote, ‘“December 7, 1941… a date which will live in infamy.” – Franklin Delano Roosevelt’. It may have been simply to commemorate the 73rd anniversary of the infamous attack, or it may be Treyarch’s way of saying that it’s going back to World War II in 2015. The Pacific-themed relevance of Pearl Harbor certainly ties into half of the campaign focus of World at War, and it was a bit jarring that the series jumped out of the Second World War and into the Vietnam War for its kind of sequel, Black Ops. There were also reports of leaked World at War II box art on Amazon last year to add fuel to the fire.On the topic of the leap from World War II to the Vietnam War, it was similarly jarring that Black Ops II zipped past the Vietnam War and went to the final years of the Cold War (1986–1989, specifically) before slowing the time-travel in 2025 for the rest of the game. There haven’t been too many games set during the Vietnam War, so there’s a whole lot of opportunity for an exploration of Call of Duty set pieces across battles that raged for close to 20 years.The soundtrack alone is worth the price of admission, with Sympathy for the Devil and Fortunate Son already used in Black Ops, but a wealth of other options taken from iconic film examples for the kind of cinematic experience that the series embraces. Outside of this, the types of warfare spanning from clearing out claustrophobic tunnels with a sidearm to booby traps lurking around every jungle corner and Vietcong ambushes, opens up possibilities for different approaches to the Call of Duty campaign gameplay formula.Then again, the Vietnam War might be a better setting for Sledgehammer Games, considering it was working on a Call of Duty game set in this era before shifting across to Modern Warfare 3.Both Black Ops titles have focused on exploring the sometimes nasty off-books operations of Special Forces groups. History has no better example of shady black ops missions than the Cold War, which earned its name because of the lack of direct military conflict. While that’s problematic for the epic all-out-war set pieces that are part and parcel of the Call of Duty formula, it does open up the series for a change of pace.A Cold War focus would lend itself to an emphasis on stealthier gameplay, and when things get loud during the campaign, it would be important to ensure that players leave no trace of their involvement in a gunfight. Ultimately, such a switch in the traditional gameplay style could feed into multiplayer, not replacing but complementing the usual online fare with different modes or tactical options for a type of player that usually doesn’t gravitate towards Call of Duty: the shadow-loving stealth player.The more we type about it, the less likely it seems as a viable option. Then again, remember that Sledgehammer Games Vietnam War-era game we mentioned in the last point? That was supposed to be a third-person shooter, so it’s clear Activision is open to the idea of trying new things with Call of Duty.The Call of Duty franchise likes to do things in threes. There were three Call of Duty games before Modern Warfare hit. Yes, it was called Call of Duty 4: Modern Warfare, but it spawned two Modern Warfare sequels for its own spin-off trilogy, and suffix numbers were dropped after the Call of Duty title from World at War onwards. Technically, Black Ops II was the end of the story that started with World at War, but the torch was passed from Viktor Reznov in World at War to Alex Mason in Black Ops, then to David Mason in Black Ops II. The problem with defining that arc as a full-fledged trilogy is that the link between World at War and Black Ops is somewhat tenuous.Reznov plays more of a cameo role in Black Ops than anything else, and he wasn’t even a playable character in World at War. That honour was with Private Dimitri “Hero of Stalingrad” Petrenko, and while he was mentioned in Black Ops, he didn’t follow the Modern Warfare tradition of passing on the protagonist torch in a Wilbur Smith’s Courtney series kind of way, whereby the main man becomes a secondary character before ultimately suffering some form of grisly death.Obscure literary references aside, if Activision chooses to pursue the magic of the number three, it’s safe to assume that Infinity Ward is developing Ghosts 2, Sledgehammer Games will be building Advanced Warfare 2 and Treyarch would upset the trinity harmony if it doesn’t make a Black Ops III. Forging such a sequel would allow Treyarch to build atop its inclusion of multiple endings, Strike Force Missions and maybe even expand the movement set with more than just a dive-to-prone option.It’s pretty safe to assume that whatever Treyarch cooks up, there will be an included Zombies mode. Such is the popularity of the cooperative horde mode that started in a two-storey house that it’s expanded to have its own mythology and Hollywood talent as playable characters. Even Sledgehammer Games has hitched a ride aboard the zombie bus in Advanced Warfare’s Exo Zombies mode. The depth of the zombie mythology in Call of Duty is so vast it shows that Treyarch has enough novel ideas to warrant a standalone title.Treyarch could retain its passion for jumping across the decades, by shifting the storyline between World War II, the Vietnam War and the Cold War, much like the developer has in its last three games. It doesn’t even need to be solely set on Earth, either, as the Moon map proved in Black Ops. It could borrow and expand upon the idea of mad scientist Edward Richtofen whose plans for power extend beyond the Second World War and even his own death.It would be a wacky departure from the mostly grounded approach to Call of Duty storytelling, but it would still allow for all of the epic set pieces and frantic shootouts that are part and parcel of the Call of Duty experience. That being said, it’s not really likely this will happen. At least fans of the cult-classic mode can rest assured Treyarch would be crazy to not expand upon the Zombie gameplay and mythology in whatever Call of Duty game does come next.So what game do you think Treyarch is working on? And what game do you wish the studio is working on?

Nathan Lawrence is a freelance games journalist based in Australia. You can chat with him on Twitter here