Air Weapons: The LWT Race

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June 4, 2019: Russia recently announced a new version of their standard APR-3 350mm (13.78 inch) LWT (lightweight anti-submarine torpedo) used mainly by sub-hunting helicopters. The new APR-3M replaces the older APR-3E. While the APR-3M is more capable than the 3E it is not much competition for the American and European LWTs. But Russia keeps trying. The APR-2 was an attempt to catch up at the end of the Cold War. Introduced in the 1980s, there was no export interest and it was mainly an effort to provide Russian ASW (Anti-submarine warfare) fixed-wing aircraft and helicopters with something better. In the 1990s the APR-3 showed up, followed by the improved APR-3E. Now, in 2019 the improved APR-3M was available and the Russian torpedo is still playing catchup. The M model weighs 470 kg (1,074 pounds), 11 percent less than the E model and can reach targets 800 meters deep. The M model is also shorter, has more range and more detection range (2,500 meters, 25 percent more than the E) and a rocket motor that can propel the LWT up to 3,000 meters from the launching helicopter or aircraft. Because of that rocket boost Russia officially calls its LWTs “missiles.”

The U.S. Navy began using its current 324mm (12.75 inch) Mk 54 LWT in 2004 and since 2010 has been upgrading these with a Mk 54 Mod 2 LWT upgrade kit that consists of a more sensitive sonar (to seek out a submarine) and more powerful computer to interpret what the sonar hears. This upgrade takes advantage of the many advances in electronic and computer components over the two decades since the current Mk 54 tech was first developed. Many components for the Mk 54 came from the older Mk 50, which ceased production in the mid-1990s. Since then, old Mk 50s have been cannibalized for parts but that supply is running out. Rather than just build more of these older components, new and improved components were designed and, as with this Mod 2 kit, used to upgrade existing Mk 54s and equip new ones.

The Mk 54 is carried mainly by aircraft but also by many American and foreign surface ships and has replaced depth charges as the main weapon against submarines. The Mk 54 is particularly effective when used by aircraft equipped to seek out submarines. Patrol aircraft can carry up to eight lightweight torpedoes, while helicopters can carry up to three (but often just one). The Mk 54 weighs about 340 kg (750 pounds) and has a warhead containing 45 kg (100 pounds) of explosives. Its guidance system has been deliberately designed to work well in shallow coastal waters, where ships are believed most likely to encounter subs. Until 1991, when the Cold War ended and the Russian nuclear sub fleet disappeared, the emphasis was on fighting subs on the high seas where the water was much deeper.

There are several upgrades available for the Mk 54. For example, to make the Mk 54 more effective on patrol aircraft, the U.S. Navy developed glide kits. Putting wings on torpedoes is all about the concern at the growing use of anti-aircraft missiles by submarines. To deal with that problem, the Navy sought to equip some Mk 54 torpedoes (that are normally dropped into the water at a low altitude by P-3 patrol aircraft) with an add-on glide kit. These systems consist of wings, control flaps, a flight control computer, battery, and GPS for navigation. The kit allows a torpedo to be released at 6,300 meters (20,000 feet), which is outside the range of submarine-launched anti-aircraft missiles, and glide for 10-15 kilometers. When down to about 100 meters (300 feet) altitude, the glide kit is jettisoned and the torpedo enters the water to seek out the sub. Normally, aircraft have to descend to under 330 meters (a thousand feet) to launch the torpedo. This takes time and puts stress on the aircraft.

Many subs have sensors that are sensitive enough to detect low flying helicopters (the main target for the subs anti-aircraft missiles) and aircraft. Patrol aircraft are more effective if they can stay at high altitude all the time. Moreover, the glide kit is easy to build, since it can use items already used for smart bombs (JDAM) and earlier glide kits.

The Mk 54 LWT cost about a million dollars each and is a cheaper and somewhat less capable replacement for the Cold War era high tech Mk 50 and the old reliable Mk 46. The Mk 54 is a more cost-effective alternative to the three million dollars Mk 50, which was in development for over two decades. The Mk 50 was difficult to build because it was meant to be a "smart" torpedo that was light enough to be carried by helicopters but could go down up to 560 meters to kill Russian nuclear subs. Alas, when the Mk 50 finally became available in the late 90s, the high-seas Russian nuclear subs were gone and the typical target was now a quieter diesel-electric sub in shallow coastal waters. So the Mk 54 was developed, using cheaper, off-the-shelf, electronic components, some technology from the Mk 50 and larger Mk 48, as well as the simpler, but not deep diving, frame and propulsion systems of the older Mk 46 lightweight torpedo. Thus the 3.25 meter (ten foot) long Mk 54 is a bit of a hybrid, created to save money and also be more capable against quieter subs operating in shallower water. The Mk 54 has a range of about 10 kilometers and a top speed of about 72 kilometers an hour. It has built-in sonar that can search for the target sub, as well as acoustic sensors (listening devices to pick up any sounds a sub might make). The Mk 54 also has an onboard computer and a data file of underwater noises and search tactics, which are used as it tries to find its target and keep after it until it can hit the sub and destroy it with the explosives in the warhead.

Since the 1960s some 25,000 of the older 230 kg Mk 46 torpedoes were manufactured. Capable of reaching targets 370 meters deep, the Mk 46 received several upgrades through 1979. A few thousand Mk 54s have been produced so far. Mk 50s are kept in inventory to deal with the few hostile nuclear subs that are still out there, although the Mk 54 also has a capability of going deep, just not as deep as the more expensive Mk 50.

China developed its own Yu-7 324mm LWT based on Italian LWTs. British, French and Italian LWTs are similar to the Mk54 but can usually go deeper (up to 1,000 meters) and get most of the export sales. The American and European LWTs have superior detection and guidance systems which receive regular upgrades.

 


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