Saddle tank (submarine)

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The German U-Boat U-995 at the German Navy memorial at Laboe, showing the starboard saddle tank as the elongated bulge along the side of the submarine

Saddle tanks are a type of ballast tank configuration fitted to some earlier submarines.

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.

The tanks themselves are usually streamlined to reduce water resistance and are prominent on many submarine designs produced prior to the end of World War II.

Saddle tanks are not fitted to current naval submarine designs as external fittings are discouraged in order to improve underwater speed and reduce hydrodynamic noise detectable by an enemy's passive-sonar. For this reason, post-1945 designs usually use internal ballast tanks, which are fitted inside the pressure hull.