a treadle assembly for throwing armor piercing shaped charges or squash charges against the underside of armored vehicles has a tripping batten connected at an angle or cant to a lever arm or leg which leg holds an armor - penetrating munition on its far end . the batten and lever arm structure is such so that the munition is oriented in the correct direction when the assembly is deployed on the surface of the ground , such as a field or roadway . the munition has a firing pin which , when armed , extends upwardly to contact the underside of the armored vehicle when the vehicle wheel or tread pushes over the treadle plate thereby pivoting the lever arm and raising the munition .