In 1972 LEGO released the 4.5V and 12V train sets as part of the Blue Era which was named because of the rail color. These train sets used additional conductor rails mounted between the standard 4.5V rails and 12V motors contained in the same housings as the 4.5V motors, but with additional metal contacts attached to the bottom of the housings.
1981 LEGO Sets
1981 strengthened the bridge from DUPLO to System through Fabuland, featuring animal characters and story-led builds. Town expanded urban life with new services and vehicles, Space continued its exploration motif with larger craft and surface equipment, and 12V Trains saw ongoing refinements for more sophisticated layouts.