Torpedo belt
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The torpedo belt was part of the armouring scheme in some warships of between the 1920s and 1940s. It consisted of a series of lightly armoured compartments, extending laterally along a narrow belt that intersected the ship's waterline. In theory, this belt would absorb the explosions from torpedoes and thus minimize internal damage to the ship itself.
Torpedo belts are also known as Side Protection Systems or SPS.
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[edit] The problem
Armoured warships (dreadnought battleships, armoured cruisers and later light and heavy cruisers) of the early 20th century carried their main protective armour above the waterline – the "main belt" – which was intended to stop flat trajectory gunfire from piercing the hull. Below the belt, the armour generally tapered away, to reduce overall weight. This, however, makes a ship vulnerable to torpedo hits below the waterline and the occasional large calibre shell. Extending the belt downwards is impractical, since this increases displacement, which increases draught and can result in reduced speed, and decreasing seaworthiness.
[edit] Solutions
Another solution is needed. Originally, torpedo nets were tried. These were simply heavy metal mesh nets hung out on booms at some distance from the ships' sides to detonate torpedoes short of the ship or even catch them. These proved largely ineffective against torpedoes since they were only deployed when stationary, were useless against shell hits below the waterline and were not effective against naval mines either. Some ships were fitted with under-water armour in vulnerable areas below the waterline. These stopped torpedoes from penetrating the ship, but the shock from the blast of underwater explosions could cause damage to the ships' weapon mountings and sensitive machinery, in addition to violently stressing the ships' structure.
[edit] Anti-torpedo bulges
With the outbreak of World War I the urgency to devise an effective torpedo defense system (TDS) was greatly increased, and the British Director of Naval Construction introduced the anti-torpedo bulge. Originally retrofitted to older ships, this was soon added to ships already under construction; in 1915 the British introduced the Renown-class battlecruisers and 1917 American Tennessee-class battleships both of incorporated anti-torpedo bulges.
[edit] Torpedo belts
It was not until 1922, in the wake of the Washington Naval Treaty that curtailed ship weights that the introduction of the British Nelson class battleships that a true layered torpedo belt was introduced. The two Nelsons used a waterfilled 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.
By the end of World War II torpedo belts, much like many of the warships they protected, were rendered obsolete by the widespread use of aircraft, and guided missiles which attacked above the belt 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.
On May 2, 1982, the ARA General Belgrano, a World War II Heavy cruiser purchased by the Argentine Navy, was sunk when hit by two conventional Mk 8 mod 4 torpedoes, despite having a protective torpedo belt. These ancient straight-running weapons of 1920s design, each with an 800 lb (363 kg) Torpex warhead, were fired by the British nuclear submarine HMS Conqueror during the Falklands War.
