By Invitation | Small is Powerful

SOV400, the small, smart, stealthy submarine


The SOV400 is a special ops diesel-electric midget submarine, designed and developed by L&T Defence—an L&T group company which has played a key role in the realisation of India’s first indigenously designed nuclear submarine. SOV400 offers best value for money, particularly for small navies with limited defence budgets, providing credible deterrence capability when pitted against powerful hegemonic neighbours.



Operational Role

A multi-role submarine, SOV400 is primarily meant for deployment and recovery of special forces while being submerged up to 40m. Its uniquely designed lock-in/lock-out system enables quick release and recovery of marine commandos, while submerged. Two 4-men Swimmer Delivery Vehicles carried on either side of the submarine can insert the divers deep inside enemy coastlines. In lieu of the SDVs, the submarine can carry ammunition and special equipment in two commando containers.

The submarine is fitted with twin torpedo tubes that can launch heavyweight torpedoes for attacks in shallow waters or in self-defence. It is also fitted with a modern conformal array sonar and advanced radio-electronic sensors for detection, surveillance, communication and interception which provide tactical information for the command through an integrated combat management system.



Being considerably small for a conventional diesel electric submarine, SOV400 has very low target strength. Normal diving depth of 125m enables undetected operations underwater. The slow turning single screw propeller with sweptback blades, microprocessor-based power convertors and carefully chosen mounting arrangement of rotating machinery and piping systems have been designed to keep underwater radiated noise within limits. The SOV400 has a streamlined external form that has been optimised for least resistance and flow noise using CFD software.


Manoeuvrability and Control

The SOV400 is designed to operate safely in coastal waters as shallow as 20m. Its cruciform-type aft control surfaces have been specially designed to meet this requirement. The submarine can hover at any depth and can be bottomed if necessary.


Control and Automation

The submarine is designed to operate with a lean crew of 12 through an integrated platform management system. All machinery and equipment located in the aft compartment can be remotely operated from the central control console located in the forward compartment

Particulars of Diesel Electric Submarine SOV400


Safety and Survivability

Hull structures (made of indigenously developed submarine grade DMR 249 steel), equipment and piping of SOV400 are designed to comply with the safety standards as per DNV GL rules for classification of naval submarines. All critical-for-safety systems have been designed to be fail-safe, ensuring uninterrupted functioning even after failure of a single component. Smoke detection and fire alarm systems, gas monitoring systems, nitrogen-based fire-fighting systems, SEIE Mk-11 suits and means for emergency escape and rescue (either through the main access trunk or through the aft escape hatch) offer adequate degree of safety and survivability of the platform and its crew.


Habitability and Ergonomics

Two AC plants of 140 kW combined cooling capacity maintain the living and operational spaces at 26 degree C even while cruising on the surface in extreme tropical seas. Quality of breathable air is maintained by the built-in oxygen regeneration system and soda lime carbon dioxide scrubbers. Fixed bunk beds have been provided for the commandos and crew, except for those on watch.


Customised Design

Since the SOV400 is a fully home-grown product, the design can be customised to suit specific requirements of the user. L&T is already working on an advanced variant with futuristic technologies including Li-lon batteries.




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