December 10,2008: A German manufacturer, Atlas, has started production of a new version of its DM2A torpedo, for use in submarines and surface ships. The DM2A4 is a 1.4 ton weapon that is the first to use fiber optic wire guidance. This makes the wire guidance immune to any electronic interference. The DM2A4 has a max range of 50 kilometers and a top speed of 90 kilometers an hour. At longer ranges, lower speed (about 60 kilometers an hour) are used. The DM2A4 has improved countermeasures and sensors. It can detect ships by detecting metal, or the wake of a surface ship. Usually, it is driven, via the wire guidance, to the general vicinity of the target, where the torpedoes sensors can take over to hit the target ship. The DM2A4 can also be used as an UUVs (unmanned underwater vehicle) for reconnaissance, and then recovered. The DM2A4 is intended for use in non-nuclear subs, mainly the German made Type 214 boats. The DM2A4 is very similar, and may be superior to, the U.S. Mk48 torpedo. This is a 1.6 ton weapon, also 533mm (21 inches) in diameter, and is used in all American nuclear subs, as well as in Australia's diesel-electric boats. A new model (Mk48-7) is in the works, which will probably match the capabilities of the DM2A4. However, the exact capabilities of modern torpedoes are classified, lest potential targets use the information to develop better countermeasures.

Although over 10,000 torpedoes have been manufactured since the end of World War II, torpedoes hardly ever get used. Submarines have only fired torpedoes in combat twice since World War II. Once in 1971, when a Pakistani (a French thousand ton Daphne class diesel-electric) sub fired three, and sank one Indian frigate and damaged another. The third torpedo failed to detonate. The second occurrence was in 1982, when a British Churchill class (4,900 ton) nuclear sub sank an Argentinean cruiser using three World War II type torpedoes. No one has yet used a modern, wire-guided torpedo to sink anything. For torpedoes, that's normal.

When the first modern torpedoes appeared in the late 19th century, it was 25 years before one was used in combat. No lightweight torpedoes (for aircraft) have been used since World War II, but thousands have been built, maintained for a decade or more, then scrapped as improved models became available.

During the past 63 years, far more  torpedoes have been expended for training and testing. But the appearance of new generations of torpedoes, and more subs, kept the torpedo manufacturers busy. Since the end of the Cold War, and the sharp drop in submarine construction, and increase in submarine retirement, the torpedo market has not done well. The main problem is that, even in normal times, most torpedoes get scraped, after two decades or so of sitting in a submarine, or a storage area of an aircraft carrier or naval air base (for lightweight torpedoes carried by helicopters and aircraft).

Torpedoes are basically robotic miniature submarines. These were the original guided missiles, although for the first sixty years, the guidance system just strove to keep the torpedo moving in a straight line. Running on batteries, modern ones can use a combination of their own sensors, or sensors aboard the sub that fired them, to find a target. In the latter case, the torpedo communicates with the sub via a thin wire. These "wire guided torpedoes" are very common, because they allow the sub to control the torpedo, if need be.

By the end of World War II, homing (usually on the noise of a ships propeller, but also the wakes of ships) torpedoes entered use. These features became standard after World War II, although high-end torpedoes now have their own sonars.

Russian torpedo makers have had a particularly rough time of it, as the Russian sub fleet suffered the most cuts when the Cold War ended. Then, and now, the Russians had developed two innovative torpedoes. One was the oversize 650mm (25.5-inch) torpedoes, which was designed to take down a U.S. aircraft carrier with one shot. Only a few Russian submarine classes can handle these oversize torpedoes. This is not a new idea, using something larger than the most common diameter (533mm, or 21 inch). During World War II, Japan frequently used, for its surface ships, a 610mm (24 inch) "Long Lance" model. This torpedo was designed to take down enemy ships, including battleships, with one hit.

The other Russian development was the rocket propelled torpedo. This, however, suffers from steering difficulties (thus it is less effective against fast moving targets) and short range (12-15 kilometers). But the high speed (360 kilometers an hour) means that these Shkval torpedoes will reach their target in about two minutes.

Russia has a wide variety of more common 533mm torpedoes, and has been selling some of them to China since (and before) 1991. But China has been developing its own torpedo manufacturing capabilities, aided by vigorous espionage activities, which have obtained much torpedo technology from the West, as well as Russia.

Most torpedoes are 533mm in diameter, about twenty feet long and weigh about 1.5 tons. These have two modes of operation. High speed mode will propel them at 80-120 kilometers an hour, but for short distances (20-40 kilometers). At slower speeds (50-90 kilometers), the range is more than doubled (70-100 kilometers). 

Lightweight torpedoes are smaller (324mm in diameter, ten feet long) and lighter (a third of a ton). They tend of have hundred pound warheads, versus 500 pound or larger for 533mm torpedoes.

More powerful batteries and electronics have been the main areas of improvement over the last decade. That, and the evolution of torpedoes into UUVs (unmanned underwater vehicles.) Just as UAVs have transformed air operations, UUVs are providing users with more control of the underwater space. After more than a century of development, torpedoes proved to be the perfect jumping off platform for developing robotic underwater vehicles. Some of these will operate from subs, launched, and even recovered, via torpedo tubes. But most UUVs are used by surface ships, aircraft and land based operations.