Aliens: Colonial Marines – AI Was Broken by a Typo

The infamously clumsy xenomorphs in Aliens: Colonial Marines may have been caused by a coding typo.

When Aliens: Colonial Marines came out in 2013 after a hideously long production, it generally provoked shudders of laughter rather than fear. Intended as a direct sequel to James Cameron’s classic Aliens, Colonial Marines at least looked the part in still photographs – but as critics and players quickly noted, the shooting action was full of glitches and bugs.

Memes and gifs featuring the xenomorphs’ less-than-threatening behavior quickly circulated, and Colonial Marines was left to shuffle off awkwardly into the mists of history.

More recently, however, there have been attempts to overhaul Colonial Marines, with modders improving its character movements and refining its graphics. In 2016, for example, we covered the work of TemplarGFX, who was working on an extensive mod that fixed the game’s particle effects, lighting, and AI. 

Taking up the baton, another Moddb user, JamesDickinson963, started combing through the original code that shipped with the game five years ago. In one config file, he found the following: 

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ClassRemapping=PecanGame.PecanSeqAct_AttachXenoToTether -> PecanGame.PecanSeqAct_AttachPawnToTeather

As you can see, the second line has a spelling error in it: “Teather” should be spelled “Tether” as in the line above. 

Intrigued, Dickinson963 fixed the typo and fired up the game to see whether it had any effect. One lonely typo couldn’t derail an entire game – could it?

As it turns out, the answer’s yes: according to him, the AttachPawnToTether bit of the code is pretty key to how the xenomorphs behave: when it’s spelled correctly, they’ll hunt and attack the player more aggressively. In the original game, they were more prone to walking in circles, bumping into things, or running away from players completely.

This discovery was made several months ago, but wasn’t brought to wider attention until it was spotted by a user on Resetera. Since then, PC Gamer has gone back to its Windows edition of Colonial Marines to run its own tests.

Sure enough, the “Teather” typo’s in there, and fixing it really does appear to make the aliens more smart and aggressive. So there we have it: Colonial Marines may have been a disappointment when it came out, but as many of us suspected, there was a far better game in there somewhere, struggling to emerge.

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