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.
1975 LEGO Sets
In 1975, LEGO continued to release a wide range of new sets and themes, including the LEGO Land Busters theme, which featured models of construction vehicles such as bulldozers and excavators. 1975 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 1975 included the LEGO Space theme, which introduced new spaceship models and minifigures, and the LEGO Castle theme, which expanded upon the castle sets released in previous years.