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.
1976 LEGO Sets
In 1976, LEGO released several new sets and themes, including the LEGO Police theme, which introduced models of police cars, motorcycles, and police stations. 1976 was also the year that LEGO introduced the LEGO Basic Building Set, which included a selection of basic bricks in various colors and shapes, as well as instruction booklets with ideas for building projects. Other notable sets and themes released by LEGO in 1976 included the LEGO Space theme, which expanded upon the Space sets released in previous years, and the LEGO Trains theme, which introduced new electric train models.