After World War II, the DB decided to use electrical traction for the main part of rail traffic, especially locos with bogies without carrying axles.
Therefore the DB ordered 5 locos with 4 different mechanical and electrical systems to test them. They came into service in 1952 and 1953, and the result of these tests was that it would not be sufficient to create only one universal locomotive, but to develop a complete line of locos which all had as many parts in common as possible. Due to these experiences there were six classes of four-axle locos built between 1956 and 1975 (110.1, 110.3, 112 (old version), 139, 140, 141 and 182), and one class of six-axle loco (the 150).
Especially the locos of class 110.1, 110.3, 112, 139 and 140 are nearly the same machines with only different gear step-ups (corresponding to the respective maximum speed) and different brake equipment (additional electrical dynamic brakes for classes 110.1, 110.3, 112 and 139), and they could therefore all be converted to each of these classes without major problems. The different locomotive bodies of 110.3 and 112 wouldn't be a problem either.
Even without the locos of class 141, 150 and 182, this was the biggest series of electrical locos in the world.
