Larsen & Toubro (L&T) has entered the niche area of midget submarine design for special operations with the SOV 400. The company, of course, has long been a part of the strategic submarine program building hulls and subsystems for the Indian Navy’s Arihant-class nuclear submarines. It is also one of the contenders for the Indian Navy’s P-75I diesel-electric submarine acquisition besides having built the Amogh, Adamya and Maya autonomous underwater vehicles (AUV) for the service. It is this pedigree that L&T is now leveraging to enter the market for midget submarines with the SOV 400.

Designed and developed in-house, the SOV 400 will be capable of carrying a crew of ten along with the ten more special operations troops. The submarine is positioned to provide smaller navies with constrained budgets an asymmetric capability. The vessel will be utilized to deploy and recover special forces while submerged for intelligences, surveillance, reconnaissance (ISR) as well as sabotage, rescue and evacuation missions.

The vessel will carry two heavyweight torpedoes outside the pressure hull for shallow-water attacks. It will be able to dive to depths greater than 100 m and travel up to 2000 nautical miles(3704 km). SOV-400 can also be carried by conventional submarines to be deployed as per mission requirements.

The 44 m long, 490 ton displacement midget submarine will have an endurance of 21 days and be able to traverse submerged for 80 nm and cruise for 2000 nm at a speed of 4 knots. Two 400 kWe generators will charge two 4 Mha lead-acid batteries. These will power a 300 kW electric motor to provide propulsion for the submarine.

A lock-in lock-out chamber will separate the two hulls of the submarine with crew and special forces personnel, combat information centre and battery banks accommodated in the forward compartment. The aft section containing machinery will be unmanned. Automation of the submarine operation will enable minimal manual operation of the submarine.

Apart from its small size and greater than 100 m operational depth, the submarine will utilise slow-turning propellers with sweptback blades and special damped mounts for machinery to achieve underwater stealth. Hull structures will be made from indigenously developed DMR 249 steel. Batteries, torpedo tubes, paints, coatings, pipes, valves, switchgear, cables, AC plants, compressors etc. will all be sourced from India.

Diesel generators will be sourced from Isotta Fraschini Motori. The permanent magnet synchronous motor (PMSM) will be sourced from Jeumont which supplies multiphase AC synchronous propulsion motors for the French Scorpene submarines. Swimmer delivery vehicle (SDV), sonar, periscope, electronic support measures (ESM), snorkel masts will also be sourced from abroad. This split once again brings to light, the need for investments and orders for domestic products to enable production of such hi-tech sub-systems in India.

While the current variant utilizes lead-acid batteries, an advanced variant with lithium-ion batteries is being developed. Apart from the Indian Navy which plans to buy such vessels, there also exists a market for such submarines in navies of friendly countries.

Preliminary design for the program has been completed and in-principle approval by DNV GL is awaited. L&T intends to complete model testing this year.

Post the 26/11 Mumbai terrorist attacks, the Indian Navy decided to procure five midget submarines for its Marine Commandos (MARCOS) to perform underwater covert operations and surveillance missions. The Navy initially planned to get five such vessels with an option to buy more later. In 2015 the Ministry of Defence finally decided to contract Hindustan Shipyard Limited (HSL) to construct two Strategic Operating Vessels (SOVs) at a cost of Rs 3,000 crore. After other shipyards like L&T objected to this move for not offering them an even playing field, the program floundered. It remains to be seen if the SOV 400 will finally fulfil the Indian Navy’s midget submarine requirements.



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