High Quality Content by WIKIPEDIA articles! A tank locomotive or tank engine is a steam locomotive that carries its water in one or more on-board water tanks, instead of pulling it behind it in a tender. It will most likely also have some kind of bunker (or oil tank) to hold the fuel. There are several different types of tank locomotive dependent upon the position and style of the water tanks and fuel bunkers. The most common type has tanks mounted either side of the boiler. This type originated about 1840 and quickly became popular for industrial tasks, and later for shunting and shorter distance main line duties. Tank locomotives have advantages and disadvantages compared to traditional tender locomotives.