When y'all meet your maker, tell him to build you some guts next time.
— The Engineer
The Operation Mecha Engine Badge is a cosmetic item for all classes. It is earned by completing your first mission of the "Operation Mecha Engine" Tour of Duty in Mann Up mode. It tracks a player's progress through the various Mann vs. Machine missions. The badge's level will increase based on the amount of times you've completed the challenges in Mann Up mode (level 100 requires completion of 297 missions).
December 20, 2012 Patch (Mecha Update)
- [Undocumented] Added Operation Mecha Engine Badge