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India enhances anti-submarine warfare capability

S. Anandan

Kochi: Even as Pakistan prides itself as the first South Asian country to commission into service a diesel-electric submarine, PNS Hamza, which has an air-independent propulsion system, India is on the threshold of perfecting its indigenous state-of-the-art underwater surveillance mechanism as part of its Anti-Submarine Warfare (ASW) programme.

Nagan, the low frequency active-cum-passive towed array sonar system developed by the Naval Physical and Oceanographic Laboratory (NPOL), Kochi, with support from industrial partners such as Bharat Electronics (BE), Larsen and Toubro (L&T), Uniflex Cables and Keltron, is in the advanced stage of user evaluation trials.

Presently, the Navy operates passive only towed array sonar system from Thales (France) onboard a few platforms such as INS Mumbai, a Delhi-class guided missile destroyer.

“Nagan marks a major technological breakthrough as it is capable of long-range detection. It is meant for fitment onboard surface ships,” NPOL Director S. Ananthanarayanan told The Hindu. The NPOL, along with the Naval Science and Technological Laboratory (NSTL), Visakhapatnam, had earlier developed Maareech, an anti-torpedo system with towed and expendable decoys. The Hindu has learnt that the Navy has already placed orders with BE for three torpedo defence systems that would be installed on ships at the Mazagaon Dock Limited.

Nagan, however, is a more complex system. “Towed array sonar system consists of a sensor array that is towed behind a submarine or surface ship. It is basically a long array of hydrophones that is trailed behind the ship using a long cable when deployed. The hydrophones are placed at equal distance on the array. This sonar is much more effective in detecting and classifying the vessels being tracked at variable depths, as noise due to turbulence of own-ship propulsion will not corrupt the signals received from the target,” said Mr. Ananthanarayanan.

“Anti-submarine warfare addresses the technological challenges of detecting quieter targets in increasingly noisy environment and the issues of detection and decoying of torpedoes. Development of passive towed array sonars during the last two decades has increased detection ranges against relatively silent submarines by an order of magnitude over the ranges obtained by the commonly used hull-mounted active sonars. Indigenous development of towed arrays over the past two decades has led to substantial competence build-up and growth of several Indian industries, in the field of electro-hydraulic winches, high density underwater connectors, electro-opto-mechanical tow cables, acoustic sensors, electronic cabinets, high performance polymer strength members and the like.”

Challenges in towed array systems lie in the deployment and retrieval of array and the understanding of the dynamic interplay of oceanic conditions and tactical scenarios. Snapping of fibre optic cable because of hydrodynamic drag and excessive deployment, and retrieval time had been major issues in the initial stages. Those, however, have been overcome.

Nagan was tested on board an offshore patrol vessel and the trials were successful.

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