What is "saddle tank"

Saddle tank may refer to:

• Saddle tank (locomotive), a water tank carried above the boiler of a steam locomotive; also the type name of a locomotive so fitted.
• Saddle tank (submarine), an early type of ballast tank
• Two "Saddle tanks" are often used by Semi-trailer trucks.

Saddle tanks are a type of ballast tank configuration fitted to mid-era submarines, those of World War II.

Saddle tanks are fitted in pairs external to the pressure hull, one on each side, in a similar manner to that of a horse's saddle-bags, the positioning of which they resemble in appearance.