Development of torpedoes

It is the height of irony that a Navy that is far short in weapons platforms that it requires to defend the nation should find itself confronted with a mismatch between arrival of platform and delivery of sensors and subsystems. If we have one we don’t have the other appears to be the ongoing syndrome for Indian Navy.

For example, India has floated the first of the Scorpene class of French submarines but it has not as yet acquired the heavy torpedoes that are its primary weaponry to destroy enemy submarines and ships.

Similarly in the case of the Kamorta class of the very latest anti-submarine warships (ASW) the towed array sensors have been acquired but not installed. These sensors help detect the presence of submarines without the need to resort to active scanners that tend to give away the position of the mother ship by the ‘ping’ that it bounces off submerged vessels as a means of detection.

Advanced weapon

India has been working on two types of torpedoes over several decades. One is the light torpedo that weighs about 220 kg that can be deployed against both surface vessels and submerged submarines with helicopters. It is known as the advanced light torpedo and is named Shyena.

The development of this weapon was initiated by the Naval Science and Technological Laboratory of the Defence Research and Development Organization in the 1990s and it took the scientists a great of experimentation to overcome a basic requirement-stability and cohesiveness of the torpedo as it was launched from high in the air and hits the water before beginning its search for the enemy submarine lurking deep in the sea. But they did succeed and they produced a projectile that can be launched both from helicopters and triple-tube ensembles on the deck of an anti-submarine warfare surface vessel like the Kamorta class of ships produced by the DRDO shipyard Garden Reach Shipbuilders and Engineers at its Kolkata dockyard.

The jolt from landing on water tended to destabilize the sensors within the torpedo and sometimes led to cracking of the casing. Finally the Indian Navy tested and approved the indigenous advanced light torpedo and it inducted 25 into service in 2012 in the first tranche. The exhilarating thing about this torpedo is that about 95 percent of its components were acquired from Indian sources while the rest-integrated circuits and sensors-are of foreign origin. The parameters are coordinated by internal computers.

Of special interest in this equipment is its ability to deal with the multiple and random existence of what are known as thermal layers beneath the sea surface which tend to bend sound ranging (sonar) waves away from the transducers and creates a false sense of absence of intruders. Some of these layers are warm and some are cool and this phenomenon creates layers within which a submarine can “hide”.

Its presence will not be detected if only active search methods are employed. Hence, more and more a dual system of active and passive sonar/sensors are employed to get a fix on enemy submarines. The Shyena torpedo is able to do just that. It is armed with a 50kg warhead and can hit targets at seven kilometers.

The other torpedo-to be used from a submerged submarine-is the heavy variety of a class beyond 1500 kg. The NSTL has been working on three prototypes of the heavy torpedo called the Varunastra. It was intended to be used in Scorpene series of attack submarines. The first of the Scorpenes is expected to join the Indian Navy after sea trials later this year but Varunastra is not ready.

During a recent trial the technology demonstrator with onboard sensors to study its health and efficiency during operations the torpedo sank in the Bay of Bengal and it took a great deal of time to locate it and salvage it.

Exploring potential

At the experimental stage the Varunastra has shown a potential of being capable of hitting a target at a range of 40 km using active/passive acoustic guidance. Its 200 kg warhead can rip a wide hole in any submarine’s double pressure hull. It is propelled by a series of silver oxide zinc batteries. While the prototypes have proved their worth it will take the better part of two years to make series production and induction of the torpedo into service.

Simultaneous, with this problem with the indigenous product is the difficulty in procuring a heavy torpedo from foreign sources. India had negotiated with the Italian firm WASS for the transfer of technology. The WASS is a subsidiary of the military complex giant Finmeccanica which was blacklisted by the Government of India for payment of bribe in the AgustaWestland VVIP helicopter deal. The ban was extended to the subsidiary as well.

The deal suffered from the liability that much of the components of the WASS torpedo had been outsourced and hence transfer of technology will be fraught with disruption and multiplicity of vendors. WASS was the lowest bidder but others in contention and relegated included the SeaHake which is said to have a range of 140 km. It also enjoys the distinction of producing all the required components-the sensor, the explosive warhead, battery, electronic systems, propulsion system, wire guidance system and propellers-are all produced by the parent company itself. So there is still an element of uncertainty about the heavy torpedo for the Scorpenes and the Arihant class of nuclear submarines, the first of which is also expected to be commissioned shortly.

Sonar technology

Before the torpedoes are launched the submarine or anti-submarine warfare (ASW) ships need to be able to find the enemy submarine. This is done either with sound ranging and navigation (Sonar) techniques wherein, very much like the radar a signal is sent out (known as the ‘ping’) and the return signal gives the range of the possible target. Ever since counter-measures have evolved acoustic targeting also involved a passive component in that sounds like the propeller signature or the engine characteristics are taken by the onboard sensor. When the torpedo is launched it operates on both signals in short bursts to confuse the target submarine.

India has developed an indigenous sonar known as the  USHUS. It was created some years ago by the Naval Physical and Oceanographic Laboratory and an indicator of its efficacy is that it is also incorporated in India’s first nuclear powered and armed submarine the Arihant.  India has recently unveiled an indigenous sonar dome which is used to cover the sonar transmitters and prevent them from becoming fouled by the marine environment. These are either bow mounted or hull-mounted and give a 180 degree horizontal field of view. Creating a sonar dome is a very specialized operation because it must be transparent for the signals to be effective.

To improve range and depth of coverage ships now trail what is known as the towed array sensors. These are hydrophones that are conjoined to a single wire and trailed far behind the ship/submarine. This helps mute the noise generated by one’s own vessel and gives a clearer picture of objects out of reach of ship borne sonar. The placement of the hydrophones tends to deal with the phenomenon of layers of different temperatures in the sea.

One hopes that for the sake of national security the mismatch between the arrival of the weapons platform and the delivery schedules of sub-systems and components is obliterated.