in 1942, significantly flooded but afloat and mobile after an impact by a
Type 93 torpedo during the
Battle of Tassafaronga. The attack claimed the lives of 125 men and injured 68. Armor, especially
spaced armor, was one of the oldest answers to the torpedo threat, developing alongside the weapon since it began to be taken seriously during the 19th century. Due to the great destructive power of a torpedo's warhead, it was not realistically possible to escape penetration after impact and detonation.
Anti-Torpedo Nets The concept of dedicated anti-torpedo armor emerged in the 1870s as the Whitehead torpedo rapidly advanced and the
torpedo boat was invented. In 1876, the British Admiralty Torpedo Committee came up with multiple ideas for deterring torpedoes, which included iron nets projected by spars, hanging like a shroud around the hull of the thus-equipped warship. The most successful of these designs consisted of galvanized iron wire rings, in diameter, interlocked together like
chainmail. Experiments were conducted in 1877, with becoming the first operational ship to be fitted with the nets. Other ideas included patrols of
picket boats around the fleet, electric
searchlights with focusable beams which can be pointed in any direction, and a
machine gun armament. Nets presented multiple drawbacks, which caused them to all but disappear from warship designs after the
First World War. The worst drawback was significant turbulence in the water, which dramatically slowed down the equipped vessels. In 1915, a report from the - a warship with a nominal top speed of - stated that with the nets deployed, their top speed was barely . Nets, when furled, caused cosmetic damage to the warship's hull, scraping away paint and exposing the hull to rust. There were also problems with spar deployment and retraction, with nets occasionally failing to retract. During the Second World War, nets were frequently relegated to protecting sheltered anchorages from torpedo attacks, as well as trespassing by enemy submarines,
human torpedoes, and
frogmen. The effectiveness of nets against torpedoes is obvious and self-evident, and they could potentially even interdict contemporary homing torpedoes, if actually struck. Nets figured for a long time as harbor defenses; as mobile defenses carried by warships, the
Royal Navy was the most prolific in their employment. Significantly, the
United States Navy never used anti-torpedo nets.
Spaced Armor Spaced armor in the context of torpedo protection is designed to increase the resiliency of a vessel once it is successfully hit by a torpedo. By the nature of the weapon, it damages its target below the
waterline, which simultaneously targets a vessel in its least armored region, and directly attacks the vessel's
capacity to remain afloat. The earliest form of dedicated anti-torpedo spaced armor was the proposal of the
double hull in 1884 by Sir
Edward Reed. This was not adopted in its pure form, since sacrificing internal hull volume was objectionable, but subsequent warship designs relocated the
coal bunkers to the periphery of the hull in order to have dual functionality as anti-flooding bulkheads with explicit consideration of the torpedo threat. Later, during the 1910s, warships progressively switched to
fuel oil, which made double hulls much more feasible and desirable. Oil-filled compartments could be placed anywhere, and seawater could be used to fill these compartments as they were gradually depleted, functioning both as ballast and absorbing the energy of a warhead blast. By the preamble to the First World War, torpedo warheads became massively destructive, both in terms of warhead filler mass and the replacement of the earlier
guncotton with superior fillers such as
TNT and
picric acid. For example, the British
21-inch Mark II carried an optional payload of of TNT, the German G6AV carried of a TNT/
HND mixture, and the Japanese
21-inch Type 43 carried of
Shimose. This prompted the design of dedicated
torpedo bulkheads. By the 1930s, warheads became even more massive, and by then all featured advanced
high explosives: the British
21-inch Mark VIII carried of
Torpex, the German
G7e carried of aluminum-augmented TNT/HND (
Schießwolle 36), and the Japanese
Type 95 carried of TNT/HND (
Type 97). Bulkhead designs became more elaborate, incorporating multiple layers, and the defensive bulkheads were organized into a fully dedicated
torpedo belt, particularly motivated by the 1922
Washington Naval Treaty which restricted warship tonnage; flooded ballast tanks and empty voids did not count toward the limit. One of the most advanced designs was the
Pugliese torpedo defense system introduced in the early 1930s, intended to protect the warship against warheads of as much as of payload. The design incorporated a series of internal drum-like cavities, oriented athwartship inside the torpedo bulkhead, surrounded by fuel or seawater ballast. Upon sustaining a blast, the affected internal cavities were expected to implode and thus absorb the energy of the blast. The most visually prominent integrated spaced armor feature was the
anti-torpedo bulge. The bulge was externally mounted and conformal to the hull, well-suited for addition to older warships as a modification. Hollow
sponsons were mounted longitudinally alongside the hull, below the waterline. The feature was introduced in 1914, as a refit, on the
Edgar-class protected cruisers designed by the
British Director of Naval Construction,
Eustace Tennyson-d'Eyncourt.
Resiliency Modifications Beyond dedicated protection schemes is the basic flotation of the vessel. The larger the vessel, the more robust it is against torpedo attack.
Hull subdivisions localize flooding, and are a feature of vessels intended to ameliorate
floodability in general. A reinforced
keel, with a double bottom which is not directly attached to it, can help avoid the keel being broken by an explosion of a
proximity-fuzed torpedo below the hull. A below-the-keel explosion is generally difficult to defend against, and efforts are best directed to other approaches, such as detection and evasion of the incoming weapon. In order to avoid disabling damage to the narrower ends of a vessel, which are the least protected by spaced armor due to their shape,
skegs can be used to retain functional shape (but not flotation) and thereby vessel mobility after a weapon hit, especially when it concerns the protection of rudders and propeller shafts. Flotation fillings can also be used as a makeshift measure; lumber and loose wooden crates were used to this extent, in order to retain some portion of buoyancy in flooded compartments after a hit.
USS Santee, a
Q-ship during the First World War, was torpedoed in 1917 while filled with wood flotation filler. The scheme worked, allowing the vessel to return to port in an awash condition. An extreme example of maximized resiliency was the abortive
Project Habakkuk aircraft carrier project, constructed (or more accurately, grown) out of
Pykrete, a composite of ice and wood pulp. The projected design had a "torpedo-proof" hull thickness of , which would have allowed it to quite simply shrug off damage inflicted by the weapons; blast craters could be patched up with more Pykrete. The overall concept became known as a
bergship, a navigable
iceberg-like vessel, which achieves flotation with its distributed bulk rather than large displacement cavities inside its hull. ==See also==