The Indian Navy (IN) is expected to soon receive its first batch of Varunastra heavyweight torpedoes developed by the Naval Science & Technology Laboratory (NSTL) of the Defence Research & Development Organization. Though developed by DRDO, the Varunastra is built by Bharat Dynamics Limited (BDL) which received an order for 63 Varunastra torpedoes as part of a contract valued at INR 1187.3 crore from the IN in June 2019. As such, BDL is expected to complete deliveries within a period of 42 months from the date of contract signature.

Varunastra is Sanskrit for ‘Varuna’s weapon‘. Varuna, for the uninitiated, is the God of the Sea in Hindu Mythology. The initial batch of the Varunastra will be deployed on board the IN’s surface warships such as the Kolkata, Rajput and Delhi-class destroyers, Kamorta-class corvettes and Talwar-class frigates in an anti-submarine warfare role. The submarine-launched version of the Varunastra is currently under development and is expected to arm the IN’s Sindhughosh (Kilo) and Arihant Classes, once that is complete.

Currently, the IN uses the following torpedoes – Whitehead A244-S, APR-3E, SET -65E/53-65KE, Type 53-65 with passive wake homing, TEST 71/76 with active and passive homing, AEG SUT Mod-1 with wire-guidance and active/passive homing, Advanced Light Torpedo Shyena.

Here’s what we know about the Varunastra so far:

The Varunastra will make India one of eight other countries to have designed and developed such a potent anti-submarine system. The ship-launched version was first conceptualized in 2007 and saw the light of the day on June 26, 2016, when it was formally inducted into the IN by the then Defence Minister, Manohar Parrikar. The Varunastra weighs 1.5 tons, and carries a 250-kg warhead. The heavyweight underwater weapon is between 23 and 26 feet long (7-8 meters) and has a diameter of 533 mm – this dimension is derived from the British 21-inch torpedo first seen in use before the First World War. The warhead is of an insensitive type that does not get triggered unless the onboard computers signal it to, making it suitable for a wide variety of combat scenarios. The torpedo shell is made of high-strength aluminum alloy, thereby giving it excellent structural rigidity and resilience to circumferential stress. The Varunastra is powered by a DRDO-developed enhanced silver oxide-zinc battery system rated at 250kW and can reach depths of up to 400 meters. The battery uses zinc as the anode, silver oxide as the cathode and potassium hydride as the electrolyte. The silver oxide-zinc battery delivers a voltage of 400V, a current of 625A and gets discharged within 5 minutes once the weapon is fully-armed. Varunastra’s batteries have a life of up to five years, and can tolerate tremendous pressure and stress. Another very important advantage of using a silver oxide-zinc battery is its excellent performance in low temperatures, making it perfect for undersea use. The Varunastra heavy-weight torpedo can reach a maximum speed of 40 knots, or 74 kmph, making it the third fastest of its kind in the world, after the Mk 48 ADCAP (Advanced Capability) and the WASS Black Shark torpedoes. Like most modern weapons of its kind, the indigineously-built Varunastra has a dual guidance system which includes wire-guidance and active-passive acoustic homing. The active acoustic homing system in the Varunastra directs itself based on the echoes received in response to sound-pulses generated on-board, much like a SONAR. The sound pulses are generated and received by pressure-transducers, and the Varunastra has three such transducers mounted on the front and on both sides of the body. When a transducer receives an echo from an object, the navigation system turns the warhead towards the source. The wire-guidance is via a thin-wire, which is also a communication medium between the torpedo and the firing ship. DRDO has also developed a 26-km-long guidance wire divided across two spools, which is being used in the Varunastra. The wire spools have a twin-core copper cable, wound in such a way that the unreeling is quick and smooth. The 26-km-wire is interconnected by an underwater connection and can take pressures of up to 40bar. The submarine-launched version of the Varunastra will be guided via a fibre-optic channel and will feature an improved front-end seeker. If the target is located at a range exceeding 40km, the torpedo uses its acoustic homing to locate it. The torpedo changes direction via hydraulically-controlled fins that adjust their position according to the homing signals received by the three pressure transducers on board. A key factor in improving the Varunastra’s performance and accuracy is the use of autonomous guidance algorithms and low-drift navigation systems. In case the enemy uses countermeasures, the Varunastra can be guided via Global Positioning System (GPS), and the DRDO claims the Indian heavyweight torpedo is the first in the world to have added this to its tech suite. The closest is the Boeing-built HAAWC ALA (High-Altitude Anti-Submarine Warfare Weapon Capability Air Launched Accessory) with GPS guidance, an add-on to the Raytheon MK 54 lightweight torpedo used in the Poseidon P8A anti-sub aircraft. The Varunastra can be used both for littoral and for deep-water defence, making it a true multi-environment weapon system. The per-unit cost of the torpedoes is up to INR 12 crore.

Adreesh Ghoshal is an automobile engineer with a deep interest in defence technology. He lives in Mumbai.



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