According to producer Drew McCoy, Respawn started with an interesting question: what would be the FPS version of mixed martial arts? So they started looking at classic titles and sub-genres, pulling in ideas from Doom, Counter Strike, Battlefield and more. "We went through a long prototyping process," says McCoy. "Our guys were trying all sorts of crazy stuff. It was all really rough, but it gave us an inkling of what could be good. And early on, one of the key things was movement, which has evolved into wall-running and double jumping - that sense of verticality. The other thing was survivability in a multiplayer game.

"The current trend is high lethality, one shot and you're down. It's popular, but if you go back 10 years, you had health and armour in Quake and Unreal, you could shoot guys 50 times - we wanted to try play with that, to lengthen the player's life without upsetting that quick kill balance. That's where the titans came in. They act as a kind of second life for you - you can take damage then eject out. Also you have AIs running around which are often easy to beat, so you get that quick kill loop."

There's also an ambition to add longevity to player vs player encounters, to get out of the twitch core rut that some well-known military shooters have ploughed. "The movement and face-off gameplay was influenced by Doom, especially the rocket launcher and plasma gun," says McCoy, "Those were projectiles that you could see coming, that you could dodge - there was this really cool back and forth dynamic. So Titans bring in a lot of that - they shoot a LOT of projectiles. And with the dash move, you can get in and out of cover real quick. This way, you're really fighting someone. It's not 'I shot first so you're dead', it's knowing the environment, knowing how to flank - we looked at a lot of old games for that."