XCOM: Chimera Squad changes a lot about classic XCOM, but the biggest departure is in the turn order itself. The decision to mix things up was controversial, and early on many members of the development team got in on the action. None carry more weight than Sid Meier, the creator of the Civilization franchise and the director of creative development at Firaxis Games. The industry legend was a big proponent of the changes, and even built a custom prototype himself.
The change to the XCOM formula in Chimera Squad is referred to as Interleaved Turns. Instead of moving all your units and then waiting for the computer to move all of its units, allied soldiers and enemy units are shuffled together in a kind of rolling initiative order. It seems like a subtle thing, but as I said in my review, it completely alters the flow of the game and helps it stand apart from other titles in the franchise. Simply put, the Interleaved Turn allows Chimera Squad to do things that no other XCOM game has been able to do before.
But even Jake Solomon, a creative director at Firaxis Games and the design lead on the entire XCOM franchise, was initially against it.
“When [they] told me they were considering initiative and interleaved actions,” Solomon said in a tweet, “I said ‘Ooooo, I don’t know that I would do that...’ And they did it anyway and it was great and clearly the right decision.”
“They” refers to Mark Nauta, the lead designer on Chimera Squad and the successful XCOM 2: War of the Chosen expansion that came before it. In an interview with Polygon, Nauta explained that his team settled on Interleaved Turns early on. But the decision was nonetheless controversial.
“Sid was actually a big proponent of that,” Nauta said. “He made me a prototype of basic XCOM with interleaved turned. It was really neat. [...] I don’t want to get into specifics, but Sid has this kind of prototype engine that he’s always doing stuff on.”
As revealed in 2016, Meier’s custom prototyping software has been in use for decades. Speaking with PCGamesN, senior producer Dennis Shirk said it’s one of his secret weapons.
“Usually he puts up a prototype,” Shirk said in an interview at E3, “nobody knows it’s coming. [...] He’ll just come to work some day and send an email through the company saying, ‘Hey, get us all together for a huge multiplayer match.’ We’ll just start playing something, and it’s really cool because he’s got his own custom engine that he works in, that he’s slowly built over the last 20-or-so-years. Then eventually it gets translated into something modern.”
No one else at Firaxis has much experience with Meier’s engine, but Nauta says he put in the time to throw his considerable expertise at the problem of Interleaved Turns. That helped prove for Nauta and his team that it would work, and enabled them to come up with other novel solutions on the way.
“Along with talking to Jake [Solomon] and I, he was a good source of feedback as well,” Nauta said, “as we were still kind of forming what some of your squad was going to be. Early in we were picking stuff that we wanted to do and we definitely wanted to shake up a log of things. It came from him and some other people, but he was a big proponent.”
Once the team settled on Interleaved Turns, lead producer Andrew Frederiksen said that much of the rest of the game began to gel. It was the backbone onto which all of the other unique features were attached. That includes the cast of human and alien soldiers, the breaching mechanic introduced to start off each combat encounter, and the overall strategic layer itself.
“It was really fun to watch it come to life,” Frederiksen told Polygon in an interview. “Interleaved was definitely not one of the first things that was there. We were talking, ‘Well, let’s do this other thing first, let’s try this.’ And they were good. ‘OK, we need to go a little further. Let’s try [Interleaved Turns].’ And we tried it, and we were like, ‘Yeah, that’s the thing.’”
Turns out that the father of Civilization, with nearly 40 years of expertise making video games, still has plenty of tricks up his sleeve.