You grind the gears of the machines and gain a damage bonus against robots. With the first rank (50 kills), you get 3% bonus to damage against all robots; the second rank (100 kills) provides a 6% bonus, and the final rank (150 kills) confers a 10% bonus.
Although there are three ranks for this perk, a bug in the reward script makes it impossible to get the third rank. The same bug also causes the notification to misreport the rank that is given. When the first rank is given, the notification says that you've been given the second rank, and when the second rank is given, the notification says that you've been given the third rank.
- On PC, this can be fixed with a mod.