What I've learned is that everything is better with a Chaos Engine, even if you don't fully understand it. Also, the power of a vehicle is directly proportional to the number of swastikas it has.
I'm sure it means something else in a different context but the only times I've seen a machine in beseige labelled a 'chaos engine' has been on giant blocks of exploding weaponry that operate for only a few seconds before reaching some kind of violent critical failure, usually resulting in the destruction of everything in the level.
>>#12, >>#10, A Chaos Engine, in the context of Besiege, can be seen as a glitch with the physics engine of the game. You basically stick a fireball onto a grabber and place several sawblades under it, all of which are connected to each other and spinning in the same direction. This produces massive amounts of torque somehow, far beyond what should be possible, enabling the creation of massively over-powered machines.