Each walker-unit was deployed on-planet by a cocoon pod, similar to the deployment of Arakyd Viper probe droids, and emerged from the impact crater fully operational. These cocoon pods encased the walker in a fluid gel that protected its descent to a planet's surface.
A droid brain in the pod controlled the speed and direction and activated decelerating thrusters shortly before impact. When the pod impacted on the surface, the bistate gel hardened, absorbing the kinetic energy and protecting the walker from damage.
MT-ATs saw action during the attempted kidnapping of Anakin Solo while he was still a baby, even though half of the force was destroyed by Admiral Gial Ackbar's FIDO unit. All but one of the vehicles were destroyed during the kidnapping attempt, thanks to sturdy Alliance defenses.