Air Assault is the movement of military forces by aircraft or helicopter to engage an destroy enemy forces or to seize and hold key terrain. In addition to regular infantry training, these forces usually receive training in rappelling and air transportation, and their equipment is sometimes modified as well to allow better transportation in aircraft. Due to the transport load restrictions of those aircraft, air assault troops are usually light infantry though light tracked armored fighting vehicles like the US M113, Russian BMD-1, German Wiesel 1 and Swedish Bv206 now enable these forces to "air-mech"; have mobility on the ground even in the face of enemy fire.