Heavyweights on the wring: in the Western World, the number of heavy torpedoes can be reckoned on one hand, yet amongst these few only a couple can be regarded as using state-of-the-art technology.

With France bailing out of the heavyweight torpedo business, we are left with the British Spearfish, the Mk 48 rood 6 and its successor the Adcap from Raytheon, the Torpedo 2000 from Saab Bofors, the Black Shark from Whitehead and the DM2 A4 rood 4 from Atlas Elektronik. Although the Torpedo 2000 features an engine of revolutionary design that makes it extremely quiet, it is like the first two mentioned, fuelled by peroxide. Quite apart from the fact that they emit gases and therefore bubbles, such propulsion systems are not devoid of risks of explosion, which nowadays makes them less desirable. This leaves us with the last two, which, by also being the most recent types and both electrically powered, are in a head-on competition.

A recent visit by the author to Atlas Elektronik's facilities helped to shed some light on what is usually regarded as a very covert activity. The first unusual feature of the DM2 A4 (known as Seahake on the export market) is its elliptical nose. This more hydrodynamic shape was made possible by the adoption of what is known as conformal sensors. Up to now, torpedoes had to be equipped with a flat sonar dome to reduce the distortional interference between the flat sensor and the surface of the dome. In the DM2 A4, there is not one sensor, but an array of these laid right against the skin of the torpedo's snout. While such a large number of sensors commands greater computing power (which is a facility that current electronics have made available) it also provides for a much wider angle of 'vision' and thereby suppresses the necessity for the torpedo to 'wiggle' to see left and right. The DM2 A4 is thus endowed with a horizontal field of view of 220 degrees. However, and because it carries three-axis laser gyros, it can turn 90 degrees on its axis to see upwards and downwards. Another advantage of the round nose is that it generates much less cavitation at high speed, notably when it comes to turning (to avoid this, flat-nosed torpedoes must first slow down).

As mentioned above, the DM2 A4 is electrically powered and uses ZnAgO (zinc/silver/oxygen) batteries. These are manufactured by Atlas (with some elements produced by Atlas' subsidiary in Greece) and are modular. The reason for this is twofold: first it was found that multiple batteries were much faster to activate than a single large unit, and such a design allows for 'trimming' the torpedo according to the mission (a serious economy for training); indeed, the DM2 A4 can be assembled in modules by navy workshops according to the required range. There is a third advantage for situations in which push might come to shove: in case of malfunction of one of the elements, the torpedo can still be allowed to swim out rather than imposing an outright and time-consuming unload and reload procedure.

The body of the DM2 A4 holds more than a mere structural role as it plays an important part in the cooling of the batteries and motor. Its elements embed a myriad tiny galleries in which the coolant flows. Because the body, which is made of aluminium, has to act as a heat exchanger, it is not painted as this would act as thermal insulator, but anodised black. In spite of the fact that the motor drives the counter-rotating propellers via a planetary reduction gear (for optimal low-speed operation) both the motor and the transmission are mechanically insulated from the frame by rubber mounts. Atlas says that it actually is quieter than the earlier model.

The DM2 A4 is linked to the submarine by an optical fibre, which poses a challenge since such tethers--while featuring an extremely high tensile strength--are very intolerant to bends and kinks which underwater currents and obstacles may combine to create. Atlas looked into several options but ended up designing its own hair-thin fibre that is able to convey data at a rate of ten megabytes per second. Interestingly, Atlas has been approached by the Royal Navy for the possibility of upgrading the copper wire of its Spearfish to fibre. Indeed, such wires also contain a fair amount of cadmium to improve their mechanical properties, which does not meet with the environmentalists' approval given the number of exercises conducted around Britain's coasts. Optical wire, on the other hand, is made of glass and returns to a natural state of silica after a few years in seawater.

Turning to the fuzing method, Atlas rejected acoustic as being too easy to fool and instead opted for a magnetic solution. One might object that this may complicate matters for a torpedo having to cope with a non-magnetic target. However, Atlas' fuze is able to detect such a target by creating induction. In other words, it transmits a magnetic field that is induced into any metal part of the target (notably its engine and transmission) and 'retrieved' by the torpedo's sensor.

The above-mentioned modularity of the DM2 A4 also offers a side application whereby the torpedo can be turned into a variety of vehicles for intelligence gathering. It must be taken into consideration that this torpedo is able to operate in depths of ten metres only. Thus the homing head and the warhead can be substituted for, inter alia, sigint equipment, including small aerials that can be discretely deployed with the torpedo body barely breaking the surface of the water.

Performance

This is always a hush-hush business when it comes to torpedoes. However, an Atlas official said that if, from a range of 20 km, a DM2 A4 is fired towards a frigate fleeing at a rate of 30 knots that target will meet with bad news within 30 minutes. The approximate speed of the torpedo is given as 50 knots.

Market

The DM2A4 has been ordered into production by the German Navy for its U212A submarines. According to Atlas, close to 90 full "wet test firings" have been performed to date. Deliveries of preproduction torpedoes for the German Navy were completed in 2003 while production deliveries are currently underway. The Turkish Navy has also adopted the model. Potential markets include Spain, India, Greece (competition was re-opened there last year against the Whitehead Black Shark due to integration costs), Brazil, Pakistan, South Korea and, in a more distant future, Singapore. Spain and Greece are expected to announce their choice this year (2005). Strangely enough, none of the latter (and neither Turkey for that matter) have requested any comparative tests with the archrival Black Shark.