Detach all train cars on the MOSCOW level.

This achievement can be unlocked towards the end of the Moscow level when you are tasked with destroying the train that is pursuing you. As you transition between the train cars, before entering the door that takes you to the next car, you can activate a switch that will release the car you came from. There are only two that you need to release and they must be done before entering the door to the next car. Look down and to the left of the door to see a prompt to release the car. The achievement will unlock after releasing the second car.