Section of Lock showing the Rack Rail over which the Towing Locomotives travel

Towing Locomotive in operation at Gatun Locks. These machines are designed to tow
vessels through the locks. There will be two locomotives ahead towing, and two astern
to retard the vessel's progress if required. In towing, they will not move faster than two
miles an hour, but a second or return track, permits them to go back at greater speed.