They say that countries used different gage tracks for their railroads so that enemy trains couldn't invade without changing wheels.
That took time, delaying them long enough for enough defensive forces to arrive.
I walk through the railroad museum, going from exhibit to exhibit wondering which trains are allies and which are enemies.
It's not easy to tell, but if you look closely, you can separate the two.
In fact, this World War II display has a friendly engine pulling three enemy boxcars.
Prisoners of war, perhaps?
They aren't talking. They're just trains in a museum, sitting on the tracks.