along the area of the ship protected by the armour belt. Most battleships built after World War I had sophisticated and complex side-protection systems, as illustrated by the cross sectional drawing of and . Torpedo belts It was not until 1922, in the wake of the Washington Naval Treaty that curtailed ship weights and with the introduction of the British s, that a true layered torpedo belt was introduced. The two Nelsons used a water-filled belt, which was written off in the tonnage limits, as water was not part of the calculations for allowed displacement. Over the next 20 years many innovative designs of TDS were tried by various nations. A warship can be seriously damaged underwater not only by torpedoes, but also by heavy naval artillery shells that plunge into the ocean very close to the targeted ship. Such shells which are usually armor-piercing shells (AP shells) can pass through a short stretch of water and strike the warship some distance below the waterline. In 1914 typical AP shells were expected to punch a hole in the exterior plate and detonate there with a destructive effect similar to a torpedo. However by the 1940s, advances in AP shell technology incorporated delayed fuses which give AP shells deep penetration capability before exploding; such AP shells will typically make a smaller hole than a torpedo in breaching a ship's hull, but detonating beyond the belt in the hull can cause splinter damage to machinery spaces and secondary magazines, which in turn compromises watertight integrity and encourages progressive flooding. To improve protection against both shells and torpedoes, an air space can be added between the torpedo belt and the hull to increase the buoyancy of the warship. Today After the end of World War II torpedo belts, much like many of the large warships they protected, were rendered obsolete by the widespread use of aircraft, and eventually—especially in the late 60s and into the 70s—by the use of anti-ship missiles, and a new generation of "smart", deep-diving torpedoes (such as the Mark 48) which are designed to detonate under a ship's keel and break its back. Citations Bibliography External links A detailed discussion of the evolution of Torpedo defense systems Naval armour Anti-submarine warfare