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Undersea sensors capability

With concerted attempts to make the oceans transparent and the development of technologies that could make the quietest of submarines detectable, India, with its nuclear doctrine predicated totally to the importance of being undetectable will have to reduce its overdependence on a submarine-based nuclear deterrence.

The “No First Strike” nuclear doctrine is based on the presumption of the inviolability of secrecy and deployability of India’s nuclear strike capability. The proviso that India would resort to massive retaliation only after absorbing a nuclear first strike is becoming increasingly flawed by the technological developments underway.

If India is to retain pre-eminence in the Indian Ocean region it will have to be able to detect and neutralize threats from foreign navies to its own submarines. Recently China has demonstrated that it will enter the Indian Ocean littoral to make a point  and it is still moot that the Chinese submarine presence was pre-notified to the Government or India came to know about it when the submarine docked in Colombo, Sri Lanka.

Such untrammeled passage through the Indian Ocean bodes ill for India. It should be able to detect and track and, if necessary, to enforce a surfacing of the foreign submarine to explain its intent and purpose. True enough the Laws of the Sea allows for free passage including through a country’s Exclusive Economic Zone but in moments of tension and hostilities these niceties can be brushed aside in the national interest.      

Sonar systems

The National Physical Oceanographic Laboratory of the DRDO has done commendable work over the years on onboard sonar detection systems and has designed and developed a family of sonars with different and mutually complementary attributes. The first of these was the Advanced Panoramic Sonar Hull mounted (APSOH) which is capable of active ranging to pinpoint location and distance, passive listening to prevent the enemy to home onto own emissions, auto tracking of targets and classification. A variant of this sonar with additional electronics and transducers for variable depth sonar (HUMVAD) has also been developed and deployed on platforms requiring such configurations. It is being produced by the Defence Public Sector Undertaking Bharat Electronics, Bangalore.

In a shining example of inhouse upgradation several Defence laboratories and the private sector have contributed to the upgradation of the APSOH to an enhanced version known as the Hull Mounted Sonar Advanced (HUMSA) imparting to the warship a panoramic sonar with fast 360 degree scan capability. This family of medium range active-cum-passive dual band sonars, optimized for both shallow and deep-water operations has proved its efficacy even in the highly variable tropical waters where sonar tends to bend on encountering the thermal layers in the sea.

HUMSA’s advanced signal processing techniques are responsible for its superior performance. The sonar uses multiple transmission modes for short and long-range surveillance. It also provides selective sector illumination to minimize interference in case of multi ship operation. The sonar can be factory-tuned to operate at any frequency. It can be configured for dual or single operator mode and hence can be fitted in ships of various tonnages. A built-in signal simulator enables the performance evaluation before sea going and also provides operator training and confidence building.

HUMSA NG is a further improvement on the  HUMSA with lower frequency transducers and state-of-the art electronics containing POWER PC processors and SHARC signal processing boards.

While the above mentioned equipment is intended for warship application the NPOL (Naval Physical Oceanographic Laboratory) has worked hard to improve the target acquisition capabilities of the ageing Soviet era Foxtrot class of submarines that were among the very first to be acquired  by India. This kind of product improvement has helped prolong the active life of the submarines even while there has been a stagnation in new acquisitions and major accidents that have sharply reduced the Indian Navy submarine fleet.

The Pachendriya sonar suite is the first indigenously developed integrated submarine sonar and tactical fire control system designed for fitment onboard Foxtrot class of submarines. This state-of-the-art system consists of passive surveillance sonar, passive ranging sonar, intercept sonar, an active sonar and underwater communication system. Operated in either single or dual operational modes, the sonar presents its vital information on four colour monitors in 13 display formats. The ergonomically designed system can automatically track up to six targets simultaneously.

The sonar is linked to a powerful tactical fire control system, which has linkages with periscope, radar and a weapon deployment controller. This facilitates rapid target acquisition and real-time attack with appropriate weapons. A built-in simulator available with the system is a powerful tool capable of simulating signals as received at the arrays and can be used for training purposes. The system has provision for online fault localization and off-line checkout facility for testing the total health of the system.

USHUS is the second submarine sonar developed with active, passive, intercept and Underwater Communication System (UCS) capabilities. These indigenous products contribute to a general roll-on initiative in creating self-reliance in major subsystems required in naval warfare.

Picking signals

However, to be able to utilize these systems effectively against any enemy, the first priority is to be able to find them and track them across the vastness of the Indian peninsular protrusion into three  extremely large water bodies-the Bay of Bengal, the Arabian Sea and the Indian Ocean. STRATEGIC AFFAIRS has on several occasions pointed to the need to utilize the undoubtedly excellent expertise available with the NPOL to create an array of sensors similar to what the Americans have been using for many decades  to detect inimical naval vehicles be they surface vessels or submarines. Described as the Transformational Reliable Acoustic Path System (TRAPS),  the Americans drop on the seabed an array of sound recorders/transmitters that pick up the propeller signature of the passing ship or submarine and transmit it to a communications node-a sonobuoy. This sets in motion a process of investigation by airborne assets and if the vessel belongs to an inimical nation it is tracked and kept under surveillance and its engine signature is recorded to know where all it has travelled.

India is fortunate in straddling one of the busiest maritime chokepoints in the Malacca Strait which connects the Pacific Ocean to the Indian Ocean. It is through this strait and the ocean space between Indonesia and Australia in the south that Chinese ships and submarines have to traverse to gain access to the Indian Ocean. Arrays of underwater listening devices at these points (which are close to the northern and southern tips of the Andaman and Nicobar Islands) could give India early warning of Chinese presence in the seas around India. Its nuclear powered submarines can come and sit in wait for hostilities to begin to show their presence. This can be aborted if the submarines can be tracked when they enter the Indian Ocean.

For network centricity and real-time location and engagement, the Indian Navy can connect the undersea arrays to their dedicated satellite with the aid of the NPOL built Tadpole sonobouys or other kinds of relay equipment to put the information on the network.

It is not as if this system is unknown to China and Pakistan and it should be expected that they too will be taking the requisite counter-measures. That could affect the efficacy of India’s nuclear deterrence posture.