As Ubisoft prepares to launch its third season, Rainbow Six: Siege is more popular than ever. But the publisher is introducing something outside of the tactical shooter’s core asymmetrical multiplayer with its new Outbreak mode. Unlike the head-to-head gameplay that has helped Siege grow to 25 million players, Outbreak has players teaming up for a cooperative horde mode.

Outbreak launches soon on the live servers, but I tried it out on the Rainbow Six: Siege test server on PC. It is a three-player mode where you team up with friends or random strangers to take on waves of zombie-like aliens. As in the competitive mode, you get to play as one of Rainbow Six hero characters, and their special powers help you survive this situation.

If you’ve played a horde mode in Gears of War, Call of Duty: Zombies, or any number of other games, you know the basic setup here. What’s nice, though, is that Siege was already a game about setting up (or infiltrating) defensive positions. So a lot of your skills translate to this more action-packed mission. For example, I played as Kapakan, who can set up booby traps on doorways and windows. This helped me take out a couple of zombies as they entered the objective area, but it maybe wasn’t as useful as setting up fortifications like wood panels on entrances and reinforced steel barriers on walls.

But unlike Call of Duty’s Zombies mode, you aren’t holding down one place for a long time. Once a wave is over, you get to freely explore the level to find the next position.

The bulk of the action, however, comes down to shooting enemies before they can disable your bomb. You need to defend that explosive so it can destroy some weird alien tentacle thing, and your gadgets will only go so far. The key to your survival definitely comes down to how capable you are at getting headshots.

I never got into Call of Duty: Zombies or Gears of War Horde Mode. While I enjoyed my time with Outbreak, it’s not going to pull me away from Siege proper. For those of you who love that kind of cooperative play, this new mode is a fun entry in that tradition.