July 8, 2011:
India is buying 32 American Mk-54 lightweight anti-submarine torpedoes to equip their eight new P-8I anti-submarine aircraft. The existing P-3 aircraft (which the P-8 is replacing) usually carries eight torpedoes. The Mk54 is a 324mm (12.75 inch) weapon, weighing about 340 kg (750 pounds) and with a warhead containing 45 kg (100 pounds) of explosives. Its guidance system has been designed to work well in shallow coastal waters. In addition, the U.S. Navy has two glide kits for air-launched anti-submarine torpedoes. Putting wings on torpedoes is all about U.S. Navy concern about the growing use of anti-aircraft missiles by submarines. To deal with that problem, it 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, down to about 100 meters (300 feet) altitude, where the glide kit would be jettisoned, and the torpedo would enter the water and seek out the sub. Normally, the P-3 has to descend to under a 330 meters (a thousand feet) to launch the torpedo. This takes time, and puts stress on the aircraft. All existing P-3s are quite old, and it will be a few years before a replacement is ready, so reducing stress on the current ones is a major issue. Indeed, it may be the main issue for introducing the glide kit. The P-3 stress problem is rather larger than the number of subs out there equipped with anti-aircraft missile systems. These systems have been around for years, and many are basically shoulder fired type missiles adapted for launch from a water-proof container that is released by a submerged sub. The P-8s are jet powered, and prefer to remain at higher altitudes.
There are other reasons for the glide kits. Many subs have sensors that are sensitive enough to detect low flying helicopters (the main target for the subs anti-aircraft missiles) and aircraft. The P-3 is also more effective if it 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 lightweight torpedo entered production seven years ago. Costing about a million dollars each, the Mk 54 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 dollar 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, and could go deep to kill Russian nuclear subs. But when the Mk 50 finally became available in the late 90s, the typical target was 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 10,000 meters and a top speed of about 72 kilometers an hour. It has a 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.
In the last 40 years, some 25,000 of the older Mk 46 torpedoes were made, and at least a few thousand Mk 54s are being manufactured. 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.