A tank of water used to determine the hydrodynamic performance of waterborne bodies such as ships and submarines, as well as torpedoes and other underwater forms. In the narrow sense, towing tanks are considered to be experimental facilities used to measure the forces, such as drag, on ship models and in turn to predict the performance of the full-scale prototype. In general, towing tanks are rectangular in planform with a uniform cross section. Different section shapes are used, ranging from rectangular to semicircular. The cross-section dimension may vary from about 8 to 52 ft (2.5 to 16 m) in width, from about 4 to 33 ft (1.5 to 10 m) in depth, and from under 100 ft (30 m) to almost 6560 ft (2000 m) in length; the size of the model varies in length from 4 to 30 ft (1.5 to 9 m).