Call of Duty 4: Modern Warfare

When you look at the most important shooting video games of all time, Call of Duty 4: Modern Warfare is near the top of the list. Its unprecedented use of cinematic storytelling and addicting multiplayer made fans grateful for Infinity Ward's decision to leave World War II behind and focus on modern-day conflicts.

However, before Infinity Ward was given the green light to work on a modern game, the studio was actually split into two teams to work on two completely distinct games: a World War II game called Call of Duty 4, and a science-fiction shooter designed specifically to compete with Microsoft's juggernaut Halo series.

According to multiplayer design director Geoff Smith, the whole team was proud of its work on Call of Duty 2, but it was difficult to compete in the mainstream as a World War II game. “All my friends were playing Halo, and I couldn’t convince them to give CoD 2 a try," he says. "I was like, 'Well, you’re this really cool spaceman who’s shooting stuff. It’s really hard for me to convince them to be cool with, like, a wooden gun with, like, a pot on your head.'"

Call of Duty 2

After the release of Call of Duty 2, Treyarch released Call of Duty 3 while Infinity Ward started work on the next entry of the series. “We didn’t know if we were going to be able to do a modern game,” studio art director Joel Emslie says. “It was a moment where we really wanted to take down Halo really bad, and we wanted to create a Halo killer. Part of the studio went off and was working on another game to do that."

That part of the team worked on the sci-fi "Halo killer" prototype, while the rest worked on the World War II version of Call of Duty 4. Unfortunately, the team quickly noticed the downsides to this plan. "The whole Infinity Ward experience is what we make is the sum of the parts, like all the components work together," Emslie says. "When you had components missing, it threw the whole thing off balance, and that’s why it was realized pretty quickly, thank God, and they brought everybody back together, and then we dug into Modern Warfare."

The decision proved to be a huge success for the studio, as Call of Duty 4: Modern Warfare ended up outselling Halo 3 head on, and the series has rarely looked back since. "It was only really when we went to modern that you felt cool," Smith says. "I think there’s a little something there where you feel cool playing, like you kind of put yourself in the situation.”

Call of Duty: Ghosts' Extinction mode

While that "Halo killer" prototype never surfaced and we never saw any kind of assets created for it, Infinity Ward did finally create a full science-fiction game with 2017's Call of Duty: Infinite Warfare. However, the developers didn't recognize any ideas or assets from the early sci-fi prototype in that game. Instead, the only thing that looked familiar to the team involved with the "Halo killer" prototype was the Crytpid alien race that served as the main antagonists in Call of Duty: Ghosts' Extinction mode.

Now, atop the industry with no worry of needing to compete with Halo, Infinity Ward pushes forward with a re-imagining of the series that put it over the top: Modern Warfare. Call of Duty: Modern Warfare launches October 25 on PlayStation 4, Xbox One, and PC.

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