When Penn Station was built, the Pennsy and LIRR also used DD1 electric locomotives to bring steam trains through the tunnels and into the station. Unlike most of today's electric engines, the DD1s used DC third rail for propulsion. There was no AC overhead wire in the station back then.
Since there would only be one or two third rail shoes on the entire consist, there were small pantographs atop those engines that contacted an overhead third rail on the ladders through the station's complex interlockings.
When the DD1s were used in freight service, they were joined with a "reacher" flat car that had four third rail shoes trainlined to the engine to permit reaching into sidings at slow speed. Third rail gaps were also designed to be much shorter in those days.
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In later years, when the M1s arrived, the railroad often operated them in four car units. Two cars regularly operated on the West Hempstead branch. Since some ten-car third rail gaps exist, the engineer had to be mindful not to "gap" his train. As the condition of the cars were allowed to deteriorate weak batteries were found to apply the brakes if the train went on a gap, rendering the train "high and dry". For many years, thereafter, few consists of less than six cars are operated.
Modern railcars roll really well too, and an MU train moving at a good clip can easily coast for many miles on its own momentum after losing power.
