One of the mules climbed a hill as the ship neared a lock gate. The mule used a gear engaging a slotted metal grove as an aid in climbing.

One of the mules had just entered a maintenance building. The mules run on tracks so are technically a railroad engine.

One of the mules had just exited the maintenance building. Notice the cables hooked on a yellow ballard while not in use guiding ships.

One of the mules was rising the last hill up to the last lock of the three Gatun Locks.

A mule passed by the operations building that had a sign showing the centennial of the canal.

Video of a mule following a ship from one lock into the next and running downhill to do so.

One of the mules that had led out a ship through the locks finally reached the end of the line. Notice the switch track so that the mules could return on the inside track and work on the outside track.

Here you can see the slotted metal in the center of the tracks. The mule engaged a gear with those slots to aid in climbing and descending. The aid was needed because the mules weigh 14 tons and the rails themselves did not provide sufficient traction.