Torpedo nets were a passive naval warship defensive device against torpedoes. Their use was common practice from the 1890s through World War II. Torpedo nets were superseded by the anti-torpedo bulge and torpedo belts.
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With the introduction of the Whitehead torpedo in 1873, and the subsequent development of the torpedo boat, new means were sought to protect capital ships against these underwater attacks. In 1876 the British Admiralty Torpedo Committee came up with a number of recommendations for combating torpedoes, which included "... nets of galvanised iron hung around each battleship from projecting 40ft spars" [1]. Experiments were conducted in 1877, with HMS Thunderer becoming the first operational ship to be fitted with the nets.
Early nets were referred to as the "Bullivant type" after the London-based company that produced them. They were constructed from 61⁄2-inch-diameter (170 mm) steel hoops linked by smaller hoops to form a mesh, with an approximate weight of one pound per square foot (5 kg/m²). These nets were projected out from the sides of the ship on 40-foot-long (12 m) wooden poles. Extensive tests were conducted, with the nets proving capable of stopping the contemporary 14-inch-diameter (360 mm) torpedo without being damaged. A 16-inch (410 mm) torpedo with a 91-pound (41 kg) warhead proved capable of causing limited damage to the net.
A heavier net was introduced in 1894 consisting of 21⁄2-inch (64 mm) hoops with a weight of five pounds per square foot (25 kg/m²).
The adoption of these nets resulted in the introduction of the torpedo net cutter on the nose of torpedoes,[2] either in the form of scissors in Japanese designs, or a French pistol-powered version.
Later heavier, denser nets used by the German and British navies were regarded as "torpedo-proof".
In addition to new tactical measures (e.g., greater harbor security and rotation of moored vessels out to sea), beginning in 1904 major navies sought a device for protection against torpedo boat attack.
Torpedo nets were the favoured solution. These were heavy steel mesh nets that could be hung out from the defending ship, when moored or otherwise stationary in the water, on multiple horizontal steel booms. Each boom was fixed to the ship at one end at or below the edge of the main deck, by a steel pin that permitted the boom to be swung against the ship and secured when the ship sailed. A series of such booms were so fixed at intervals along each side of the ship. When the ship was moored, the free ends of the booms could be swung out with the net hung on the outer ends, thus suspending the net at a distance from the ship equal to the length of the boom, all around the ship. With the net mounted, a torpedo aimed at the ship would hit the mesh net and explode at a sufficient distance from the hull to prevent serious damage to the ship.
The first major use of torpedo nets was during the destroyer torpedo attack on the Imperial Russian Navy (IRN) stationed at Port Arthur on 08 February 1904; these were the opening shots of the Russo-Japanese War, conducted by the Imperial Japanese Navy (IJN). Although it was a surprise attack, Russian naval intelligence had somewhat prepared for such an attack by conducting naval maneuvers, in which Russian destroyers practiced attacks against their battleships, however, the IRN didn't know when that attack would actually come.[3] Consequently, the IJN had planned on the IRN battleships to have had their torpedo nets deployed when they launched their attack, and ordered "net cutters" to be attached to their torpedoes.[4]
IJN destroyer captains had used net cutters during maneuvers and considered that net cutters were ineffective and caused stability problems for their torpedoes.[5] Regardless, the order was given to install them, and the destroyers were to close onto their targets (the Russian battleships) at maximum speed before launching their "yellow cigars"[6] at a range of about 200 meters.[7]
During the actual attack on 08 February, three of the four destroyers planted their torpedoes into the waiting torpedo nets, as none of the net cutters had worked.[8] Destroyer captains reported seeing "bubbles rising from the water alongside the net which held the torpedoes firmly suspended by their heads."[9] The primary targets, the cruiser Pallada and the battleships Tsesarevich and Retvisan, received only moderate damage as the nets had protected their vital areas, leaving primarily their bows and stern sections unprotected. Destroyer captains reported that, if the Japanese net cutters had worked or the Russian nets had not been deployed, the Japanese torpedoes would have sunk all three Russian warships.[10] After the attack, the IJN issued a new style net cutter, but it was already known that the Russian navy would not be caught by surprise again; and, if a ship was underway, it would not use torpedo nets.[11]
During other actions later in the war nets were used effectively by the battleship Sevastopol. At the end of the siege of Port Arthur, that vessel was anchored outside the harbor in a position where she was sheltered from the fire of the Japanese batteries but became exposed to persistent attacks from torpedo boats. From 11 to 16 December 1904, Sevastopol was exposed to numerous night attacks. The Japanese employed no less than 30 torpedo-boats, of which two were lost, and it was estimated that altogether 104 torpedoes were fired against the ship. One torpedo exploded in the nets near the bow and produced a leak in the torpedo room; another damaged the compartment forward of the collision bulkhead, because the nets yielded to such an extent that the explosion took place near the hull. The last two torpedoes that struck the ship were fired at close range against the unprotected stern: they damaged the rudder and produced a serious leak under the quarterdeck, so that the aft end of the ship sank until it touched the bottom. The leak was repaired. The ship again floated and on the last day of the siege she was taken out to deep water and sunk.
The sinking by torpedo of three Allied battleships during the 1915 Dardanelles Campaign, all with torpedo nets deployed, demonstrated that the increased speed of newer torpedoes and the tactic of firing several torpedoes at the same location on the target had made the torpedo net ineffective.
Torpedo nets were superseded by the anti-torpedo bulge and torpedo belts.
However, torpedo nets continued in use during World War II to protect ships at anchor, especially as obstacles against submarines, human torpedoes, and frogmen. They were also used to protect dams, and led to the development of bouncing bombs to defeat them, as in Operation Chastise.