In early 2017 Burma ordered $40 million worth of the new Indian made Shyena lightweight anti-submarine torpedo. This is the first export sale and the Indian Navy has apparently only received a few dozen of them. For India Shyena replaces the Italian A244S, a 254 kg (559 pound) model widely used (by 16 nations) since the early 1980s model. These smaller torpedoes are used mainly for anti-submarine warfare and are usually fired from helicopters, naval patrol aircraft or warships. India bought 450 of the A244S but obtained a license to manufacture their version (called NST58) in India and because of that was able to develop local suppliers for nearly all the components.
Shyena was supposed to be an improved A244S but apparently was that in name only and not as capable as the latest MK 3 version of the A244S, which has a longer range (13.5 kilometers compared to six kilometers) and a much more effective sensor and guidance system. In 2012, after two decades of development, India put Shyena into production and at least 25 were delivered to the Indian Navy for use on helicopters.
Meanwhile in 2011 India ordered 32 American Mk54 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, like Shyena, 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 like the Mk54. 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 Mk54 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 an Mk54 torpedo. This takes time, and puts stress on the aircraft. Reducing stress on these larger maritime patrol aircraft was apparently one reason for introducing the glide kit. There apparently not a lot 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 Mk54 lightweight torpedo entered production in 2003 and is a good example of how to handle development of systems like this. Costing about a million dollars each, the Mk54 is a cheaper, and somewhat less capable replacement for the Cold War era high tech Mk50 and the old reliable Mk46. The Mk54 is a more cost effective alternative to the three million dollar Mk50, which was in development for over two decades. The Mk50 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 Mk50 finally became available in the late 90s, the typical target was a quieter diesel-electric sub in shallow coastal waters. So the Mk54 was developed, using cheaper, off-the-shelf, electronic components, some technology from the Mk50 and larger Mk48, as well as the simpler, but not deep diving, frame and propulsion systems of the older Mk46 lightweight torpedo. Thus the 3.25 meter (ten foot) long Mk54 is a bit of a hybrid, created to save money, and also be more capable against quieter subs operating in shallower water. The Mk54 has a range of about ten kilometers 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 Mk54 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 Mk54s have been manufactured. Mk50s are kept in inventory to deal with the few hostile nuclear subs that are still out there, although the Mk54 also has a capability of going deep, just not as deep as the more expensive Mk50.
There is still a market for lightweight torpedoes that are produced in smaller quantities. A few thousand built and sold over a decade or so is economically viable. This was the case with the A244S and similar models from European nations. China also developed its own lightweight torpedo based on some A244S ones it bought. In addition to selling the torpedoes the manufacturer makes a lot of money selling upgrades, customer modifications and maintenance and repair services. Most of these torpedoes are never used as intended and eventually retired when they are so old they are unreliable and not worth refurbishing. In light of all this India will have a difficult time establishing Shyena as a economically and militarily worthwhile effort.