The modern torpedo (historically called an automotive, automobile, locomotive, or fish torpedo) is a self-propelled explosive projectile weapon, launched above or below the water surface, propelled underwater toward a target, and designed to detonate on contact or in proximity to a target. The original use of "torpedo" was for a variety of devices that would today be mostly called a "mine". However, from the First World War onwards "torpedo" was only used for an underwater self-propelled missile, often called colloquially a "fish".
While the battleship had evolved primarily around engagements between armoured ships with large guns, the torpedo allowed torpedo boats, other lighter surface ships, submersibles, and aircraft to destroy large armored ships without large-caliber guns, though sometimes at the risk of being hit by longer-range shellfire. In the Battle of Samar, destroyer-mounted torpedoes were the only weapons available to the U.S. task force capable of damaging opposing Japanese cruisers and battleships.
Today's torpedoes can be divided into lightweight and heavyweight classes; and into straight running, autonomous homers and wire-guided ones. They can be launched from a variety of platforms. Originally, the torpedo was primarily used in an anti-shipping role. This has been largely superseded by the missile, so the torpedo's main contemporary use is against submarines.
Torpedoes may be launched from submarines, surface ships such as torpedo boats and destroyers, helicopters and fixed-wing aircraft, unmanned naval mines and naval fortresses. They are also used in conjunction with other weapons; for example the Mark 46 torpedo used by the United States becomes the warhead section of the ASROC (Anti-Submarine ROCket) and the CAPTOR mine (CAPsulated TORpedo) is a submerged sensor platform which releases a torpedo when a hostile contact is detected.
Much like the invention of the helicopter, the earliest torpedo concepts existed many centuries before being developed as working devices. The earliest known description is found in the work of Syrian engineer Hassan al-Rammah in 1275. His works show illustrations of a rocket-propelled device that appears to have been designed to move on the surface of water.
Although the term "torpedo" was not coined until 1800, the early submarine Turtle attacked using an explosive very similar in intent and function. Turtle dived under a British vessel to attach a bomb by means of an auger. The bomb was to be detonated by a timed fuse, probably a type of clockwork mechanism. In its only recorded attack, Turtle failed to penetrate the hull of HMS Eagle, which had been copper-plated to resist shipworms.
The first usage of the term torpedo to refer to a naval explosive was by American inventor Robert Fulton. In 1800, Fulton launched his submarine, Nautilus, and demonstrated its method of attack using a floating explosive charge Fulton called a torpedo. The submarine would tow the torpedo, submerging beneath an enemy vessel and dragging the torpedo into contact with it. Fulton successfully destroyed demonstration targets in both France and Britain, but neither government was interested in purchasing the vessel and Fulton's experiments ceased in 1805.
During the American Civil War, the term torpedo was used for what is today called a contact mine, floating on or below the water surface using an air-filled demijohn or similar flotation device. (As self-propelled torpedoes were developed the tethered variety became known as stationary torpedoes and later mines.) Several types of naval "torpedo" were developed and deployed, most often by the Confederates, who faced a severe disadvantage in more traditional warfare methods.
In this period, "torpedoes" floated freely on the surface or were bottom-moored just below the surface. They were detonated when struck by a ship, or after a set time, but were unreliable. These could be as much a danger to Confederate as to Union shipping, and were sometimes marked with flags that could be removed if Union attack was deemed imminent. Rivers mined with Confederate torpedoes were often cleared by Unionists placing captured Confederate soldiers with knowledge of the torpedoes' location in small boats ahead of the main fleet.
"Torpedoes" (mines) could also be detonated electrically by an operator on shore (as demonstrated also by Fulton), so friendly vessels or low-value enemy vessels could be ignored while waiting for the capital ships to sail over them. However, the Confederacy was plagued by a chronic shortage of materials including platinum and copper wire and acid for batteries, and the wires had a tendency to break. Electricity was a new technology, and the limitations of direct current for effective distance was poorly understood, so failures were also possible because of the decrease in voltage when the torpedoes were placed too far from the batteries. Former United States Navy Commander Matthew Maury, who served as a commander in the Confederate Navy, worked on the development of an underwater electrical mine.
David Farragut encountered tethered and floating contact mines in 1864 at the American Civil War Battle of Mobile Bay. After his leading ironclad, USS Tecumseh, was sunk by a tethered contact mine (torpedo), his vessels halted, afraid of hitting additional torpedoes. Inspiring his men to push forward, Farragut famously ordered, "Damn the torpedoes, full speed ahead!"
The first torpedo designed to attack a specific target was the spar torpedo, an explosive device mounted at the end of a spar up to 40 feet (12 m) long projecting forward underwater from the bow of the attacking vessel. When driven up against the enemy and detonated, a hole would be caused below the water line. Spar torpedoes were employed by the Confederate submarine H. L. Hunley, as well as by David-class torpedo boats, among others. However, these torpedoes were liable to cause as much harm to their users as to their targets.
During the US Civil War, the term "torpedo" was also used to refer to various types of bombs and boobytraps. Confederate General Gabriel J. Rains deployed "sub-terra shells" or "land torpedoes", artillery shells with pressure fuses buried in the road by retreating Confederate forces to delay their pursuers. These were the forerunners of modern land mines. Union generals publicly deplored this conduct.
Confederate secret agent John Maxwell used a clockwork mechanism to detonate a large "horological torpedo" (time bomb) on August 9, 1864. The bomb was hidden in a box marked "candles" and placed aboard a barge containing Union ammunition (20,000–30,000 artillery shells and 75,000 small arms rounds) moored at City Point, Virginia, on the James River. The explosion caused more than US$2 million in damage and killed at least 43 people.
The coal torpedo was a bomb shaped like a lump of coal, to be hidden in coal piles used for fueling Union naval vessels. The bomb would be shoveled into the firebox along with the real coal, causing an explosion. Although the North referred to the device as the coal torpedo in newspaper articles, the Confederates referred to it as a "coal shell".
From World War I onwards, the word torpedo was used only for self-propelled projectiles that travelled under or on water.
The first working prototype of the modern self-propelled torpedo was created by a commission placed by Giovanni Luppis (Ivan Lupis), an Austrian naval officer from Fiume (today Rijeka, Croatia), a port city of the Austrian Empire, on Robert Whitehead, an English engineer who was the manager of a Fiume factory. In 1864, Luppis presented Whitehead with the plans of the salvacoste (coastsaver), a floating weapon, driven by ropes from the land, and made a contract with him in order to perfect the invention.
Whitehead was unable to improve the machine substantially, since the clockwork motor, the attached ropes and the surface attack mode all contributed to a slow and cumbersome weapon. However, he kept considering the problem after the contract had finished, and eventually developed a tubular device, designed to run underwater on its own, and powered by compressed air.
Maintaining proper depth was a major problem in the early days but Whitehead introduced his "secret" in 1868 which overcame this. It was a mechanism consisting of a hydrostatic valve and pendulum which caused the torpedo's hydroplanes to be adjusted so as to maintain a preset depth.
After the Austrian government decided to invest in the invention, Whitehead started the first torpedo factory in Fiume. In 1870, they improved the devices to travel up to approximately 1000 yards (914 m) at a speed of up to six knots, and by 1881 the factory was exporting its torpedoes to ten other countries. The torpedo was powered by compressed air and had an explosive charge of gloxyline (gun-cotton). Whitehead went on to develop more efficient devices, demonstrating torpedoes capable of 18 knots (1876), 24 knots (1886), and finally 30 knots (1890).
Royal Navy representatives visited Fiume to see a demonstration in late 1869 and in 1870 a batch of torpedoes was ordered. In 1871, the British Admiralty paid him £15,000 for certain of his developments and production started at the Royal Laboratories in Woolwich the following year. In 1893, RN torpedo production was transferred to the Royal Gun Factory. The British later established a Torpedo Experimental Establishment at HMS Vernon and a production facility at the Royal Naval Torpedo Factory, Greenock in 1910. These are now closed.
Whitehead opened a new factory near Portland harbour, England in 1890, which continued making torpedoes until the end of the Second World War. Because orders from the RN were not as large as expected, torpedoes were mostly exported. A series of devices was produced at Fiume, from 14" upward. The largest Whitehead torpedo was 18 inches (457 mm) in diameter and 19 feet (5.8 m) long, made of polished steel or phosphor-bronze, with a 200 lb (90 kg) gun-cotton warhead. It was propelled by two propellers driven by a three-cylinder Brotherhood engine, using compressed air at around 1300 lbf/in² (9 MPa). The torpedo was designed to self-regulate its course and depth as far as possible. By 1881, nearly 1500 torpedoes had been produced. Whitehead also opened a factory at St Tropez in 1890 which exported torpedoes to Brazil, Holland, Turkey and Greece. Whitehead faced competition from the American Lieutenant Commander John A. Howell, whose own design, driven by flywheel, was simpler and cheaper. It was produced from 1885 to 1895, and left no wake and ran straight. A Torpedo Test Station had been set up on Rhode Island in 1870, and an automobile torpedo produced in 1871 but this was unsuccessful. The Lay torpedoes were also largely unsuccessful as were various privately invented ones. The Howell torpedo was the only USN one until Whitehead torpedoes produced by Bliss and Williams (later E W Bliss and Co) came into service in 1894. Five varieties were produced, all 45 cm diameter. An improved version, the Bliss-Leavitt,with a turbine engine was later produced, some with a larger diameter. Various versions were used in both World War I and World War II.
Whitehead purchased rights to the gyroscope of Ludwig Obry in 1888 but it was not sufficiently accurate, so in 1890 he purchased a better design (ironically from Howell) to improve control of his designs, which came to be called the "Devil's Device". The firm of L. Schwartzkopf in Germany also produced torpedoes and exported them to Russia, Japan, and Spain. In 1885, Britain ordered a batch of 50 as torpedo production at home and at Fiume could not meet demand.
On 16 January 1878, the Turkish steamer Intibah became the first vessel to be sunk by self-propelled torpedoes, launched from torpedo boats operating from the tender Velikiy Knyaz Konstantin under the command of Stepan Osipovich Makarov during the Russo-Turkish War of 1877-78. In another early use of the torpedo, Chilean ship Blanco Encalada was sunk on April 23 1891 by a torpedo from the gunboat Almirante Lynch, during the Chilean Civil War.
By this time the torpedo boat, the first of which had been built at the shipyards of Sir John Thornycroft in 1877, had gained recognition for its effectiveness, and the first torpedo boat destroyers (later simply destroyers) were built to counter it. Torpedoes were also used to equip gunboats of around 1,000 tons, thus becoming torpedo gunboats.
Originally, torpedoes were designed to be straight running, though this was not always the case in practice. Around 1897, Nikola Tesla patented a remote controlled boat and later demonstrated the feasibility of radio-guided torpedoes to the United States military.
Torpedoes were widely used in the First World War, both against shipping and against submarines. Germany and its allies disrupted the supply lines to Britain largely by use of submarine torpedoes (though submarines also extensively used guns).) Britain and its allies also used torpedoes throughout the war. U-boats themselves were often targeted, twenty being sunk by torpedo.
Originally the Japanese Navy purchased Whitehead or Schwartzkopf torpedoes but by 1917 they were conducting experiments with oxygen as a fuel. Because of explosions they abandoned the experiments but resumed them in 1926 and by 1933 had a working torpedo. They also used conventional wet-heater torpedoes.
In the inter-war years, tight budgets caused nearly all navies to skimp on testing their torpedoes. As a result, only the Japanese had fully-tested torpedoes (in particular the Type 93) at the start of World War II. The lack of reliability caused major problems for the American Submarine Force in the initial years of the American involvement in World War II, primarily in the Pacific War.
All classes of ship, including submarines, and aircraft were armed with torpedoes. Naval strategy at the time was to use torpedoes, launched from submarines or warships, against enemy warships in a fleet action on the high seas. Targeting unarmed enemy merchant shipping was prohibited by rules of war. (In the event, merchantmen were armed and acted as de facto naval auxiliaries, rendering the distinction moot.) There was concern torpedoes would be ineffective against warships' heavy armor; an answer to this was to detonate torpedoes underneath a ship, badly damaging its keel and the other structural members in the hull, commonly called "breaking its back". This was demonstrated by magnetic influence mines in World War I. The torpedo would be set to run at a depth just beneath the ship, relying on a magnetic exploder to activate at the correct time. Germany, Britain, and the U.S. independently devised ways to do this; German and American torpedoes, however, suffered problems with their depth-keeping mechanisms, coupled with faults in magnetic pistols shared by all designs.
Inadequate testing had failed to reveal the effect of the earth's magnetic field on ships and exploder mechanisms, which resulted in premature detonation. The Kriegsmarine and Royal Navy promptly identified and eliminated the problems. In the United States Navy, there was an extended wrangle over the problems plaguing the Mark 14 torpedo (and its Mark 6 exploder). Cursory trials had allowed bad designs to enter service. Both the Navy Bureau of Ordnance and the United States Congress were too busy protecting their own interests to correct the errors, and fully-functioning torpedoes only became available to the USN twenty-one months into the Pacific War.
British submarines used torpedoes to interdict the Axis supply shipping to North Africa and the Fleet Air Arm Swordfish sank three Italian battleships at Taranto by torpedo. Torpedoes were used by British surface vessels to help finish off the German battleship Bismarck. Large tonnages of merchant shipping were sunk by submarines with torpedoes in both the Battle of the Atlantic and the Pacific War.
Torpedo boats such as the American PT boats enabled relatively small but fast boats to carry enough firepower to theoretically destroy a larger ship, though this rarely occurred in practice. Destroyers of all navies were also usually armed with torpedoes to attack larger ships. In the Battle off Samar, destroyer-mounted torpedoes of the American task force "Taffy 3" showed effectiveness at defeating armor. Damage and confusion caused by torpedo attacks were instrumental in beating back a superior Japanese force of battleships and cruisers.
Later in the Second World War, torpedoes were given acoustic (homing) guidance systems, originally by the Germans in the G7es torpedo. Pattern-following and wake homing torpedoes were also developed. Acoustic homing formed the basis for torpedo guidance after the Second World War. Though Lupis' original design had been rope guided, torpedoes were not wireguided until the 1960s. Because of improved submarine strength and speed, torpedoes had to be given improved warheads and better motors. During the Cold War, torpedoes were an important asset with the advent of nuclear powered submarines, which did not have to surface often, particularly those carrying strategic nuclear missiles.
At higher pressures the cooling experienced by the air as it expanded in the engine caused icing problems (see adiabatic cooling). This was remedied by heating the air with seawater before it was fed to the engine, which increased engine performance further, because the air expanded even more after heating. This was the principle used by the Brotherhood engine.
A derivative of the compressed-air torpedo was the steam torpedo. Developed by Vickers Ltd, it mixed alcohol (first ethanol, later methanol) with compressed air in the combustion chamber, producing steam. This increased speed, but produced a visible wake.
Germany introduced its first battery-powered torpedo shortly before World War II, the G7e. It was slower and had shorter range than the conventional G7a, but was wakeless and much cheaper. Its lead-acid rechargeable battery was sensitive to shock, required frequent maintenance before use, and required preheating for best performance. The experimental G7ep, an enhancement of the G7e, used primary cells.
The United States copied the German design (although with improved batteries) to produce the Mark 18 Torpedo and further refined it to produce the FIDO air-dropped acoustic homing torpedo for anti-submarine use.
Modern electric torpedoes such as the Mark 24 Tigerfish or DM2 series commonly use silver oxide batteries which need no maintenance, allowing torpedoes to be stored for years without losing performance.
The Victorian era Brennan, which could be steered onto its target by varying the relative speeds of its contra-rotating propellers. However the Brennan required a substantial infrastructure and was not suitable for ship-board use. Therefore, for the first part of its history, the torpedo was guided only in the sense its course could be regulated so as to achieve an intended impact depth (due to the sine wave running path of the Whitehead, this was a hit or miss proposition, even when everything worked correctly) and, through gyroscopes, a straight course. With such torpedoes the method of attack in small torpedo boats, Torpedo bombers and small submarines, was to set on a collision course abeam to the target and to release the torpedo at the last minute, before peeling away; all the time running a gauntlet of defensive fire.
In larger ships and submarines, fire control calculators gave a wider engagement envelope. Originally, plotting tables (in large ships), combined with specialised slide rules (known in U.S. service as the "banjo" and "Is/Was"), reconciled the speed, distance, and course of a target with the firing ship's speed and course, together with the performance of its torpedoes, to provide a firing solution. By the Second World War, all sides had developed automatic electro-mechanical calculators, exemplified by the U.S. Navy's Torpedo Data Computer. Submarine commanders were still expected to be able to calculate a firing solution by hand as a back up against mechanical failure, and because many submarines existing at the start of the war were not equipped with a TDC; most could keep the "picture" in their heads and do much of the math (which was simple trigonometry) without recourse to paper calculations, from extensive training.
Against high value targets and multiple targets, submarines would launch a spread of torpedoes, to increase the probability of success. Similarly, squadrons of torpedo boats and torpedo bombers would attack together creating a "fan" of torpedoes across the target's course. Faced with such an attack, the prudent thing for a target to do was to turn 90 degrees to its original course and steam away from the torpedoes and the firer, allowing the relatively short range torpedoes to use up their fuel. An alternative was to "comb the tracks", turning 90 degrees towards the torpedoes. The intention of such a tactic was still to minimise the size of target offered to the torpedoes, but at the same time be able to aggressively engage the firer. This was the tactic advocated by critics of Jellicoe's actions at Jutland, his caution at turning away from the torpedoes being seen as the reason the Germans escaped.
The use of multiple torpedoes to engage single targets greatly reduces a submarine's combat endurance and its ability to stay on patrol. This can be improved by ensuring a target can be effectively engaged by a single torpedo, which gave rise to the guided torpedo. Guided torpedoes can use passive or active guidance, or a mix of the two. Passive acoustic torpedoes home in on emissions from a target. Active acoustic torpedoes home in on the reflection of a signal, or "ping", from the torpedo or its parent vehicle; this has the disadvantage of giving away the presence of the torpedo. In semi-active mode, a torpedo can be fired to the last known position or calculated position of a target, which is then acoustically illuminated ("pinged") once the torpedo is in attack range.
Torpedoes can operate on a fire and forget principle or be controlled by its firing vessel. During the Second World War, the U.S. experimented with frequency hopping radio controlled torpedoes using matching pairs of punched card rolls based on those of player pianos. Modern torpedoes use an umbilical wire; the advantage of the umbilical is the vastly greater computer processing power of the submarine or ship can be used. Torpedoes such as the U.S. Mark 48 can operate in a variety of modes increasing tactical flexibility.
Torpedoes are launched several ways:
Many navies have two weights of torpedoes:
In the case of deck or tube launched torpedoes, the diameter of the torpedo is obviously a key factor in determining the suitability of a particular torpedo to a tube or launcher, similar to the caliber of the gun. The size is not quite as critical as for a gun, but diameter has become the most common way of classifying torpedoes.
Length, weight, and other factors also contribute to compatibility. In the case of aircraft launched torpedoes, the key factors are weight, provision of suitable attachment points, and launch speed. Assisted torpedoes are the most recent development in torpedo design, and are normally engineered as an integrated package. Versions for aircraft and assisted launching have sometimes been based on deck or tube launched versions, and there has been at least one case of a submarine torpedo tube being designed to fire an aircraft torpedo.
As in all munition design, there is a compromise between standardisation, which simplifies manufacture and logistics, and specialisation, which may make the weapon significantly more effective. Small improvements in either logistics or effectiveness can translate into enormous operational advantages.
Some common torpedo diameters (using the most common designation, metric or inch, and listed in increasing order of size):
Even larger sizes of torpedo tube, including 660 mm (26 inches), 762 mm (30 inches), and 916 mm (about 36 inches), have been installed on some nuclear submarines. These tubes are designed to be capable of firing large diameter munitions such as cruise missiles, as well as the standard 21 inch heavy torpedo.
The torpedoes used by the World War II Kriegsmarine included:
Originally, Whitehead torpedoes were intended for launch underwater and the firm was upset when they found out the British were launching them above water, as they considered their torpedoes too delicate for this. However, the torpedoes survived. The launch tubes could be fitted in a ship's bow, which weakened it for ramming, or on the broadside; this introduced problems because of water flow twisting the torpedo, so guide rails and sleeves were used to prevent it. The torpedoes were originally ejected from the tubes by compressed air but later slow burning gunpowder was used. Torpedo boats originally used a frame which dropped the torpedo into the sea. Royal Navy Coastal Motor Boats of WW1 used a rear-facing trough and a cordite ram to push the torpedoes into the water tail-first.
Developed in the run up to Second World War, multiple-tube mounts (up to quintuple in some ships) for 21" to 24" torpedoes in rotating turntable mounts appeared. Destroyers could be found with two or three of these mounts with between five and twelve tubes in total. The Japanese went one better, covering their tube mounts with splinter protection and adding reloading gear (both unlike any other navy in the world), making them true turrets and increasing the broadside without adding tubes and top hamper (as the quadruple and quintuple mounts did). Considering their Type 93s possible war winners, the IJN equipped their cruisers with torpedoes. The Germans also equipped their capital ships with torpedoes.
Smaller vessels such as PT boats would carry their torpedoes in fixed deck mounted tubes using compressed air. These were either aligned to fire forward or at an offset angle from the centerline.
Late in the war lightweight mounts for 12.75" homing torpedoes were developed for anti-submarine use consisting of triple launch tubes used on the decks of ships. These were the Mark 32 launcher in the USA and part of STWS (Shipborne Torpedo Weapon System) in the UK. Later a below-decks launcher was used by the RN. This basic launch system continues to be used today with improved torpedoes and fire control systems.
Late in World War Two, the U.S. adopted a 16" (40cm) homing torpedo for use against escorts.