| 摘要 |
A track-mounted vehicle having legs which can be retracted or extended, so that the vehicle can be raised to permit advancement of the track and then lowered, the vehicle either being raisable off the track to permit advancement, or having captivating means by which the track is raised, together with the vehicle, the track and the vehicle having rack-and-pinion or rack-and-chain drive means so that, in the raised position, the track can be advanced by said drive means and, in the lowered position, the vehicle is movable along the track by said drive means. |
