First reported by the Delhi Defence Review site on July 17 2021, the SOV-400 is a new submarine design from Larsen & Toubro. As it's name implies it is around 400 tons placing it at the larger end of the 'midget submarine' spectrum.

The SOV-400 appears optimized for Special Forces missions, carrying 10 SF operators. Two 4-person SDVs (Swimmer Delivery Vehicles) can be hung on the lower hull. This gives the SF combat swimmers a means to conduct longer-endurance missions. So for a cross-beach mission a 4-6 person team could be inserted by the two SDVs, with two remaining as drivers. 2 more SF personnel would remain aboard the SOV-400 to coordinate and support the mission.

For self-defence, or targets of opportunity, the SOV-400 is armed with two 533mm (21") heavyweight torpedoes carried externally. There is a modest sonar in the bow, but logically this will primarily be for surface targets. The exact model of torpedo is unspecified and likely to be adaptable to customer needs.

SOV-400 Specifications

Displacement: <490 tons surfaced, <550 tons submerged
Length: 44 m
Beam: 4.3 m
Operating Depth: 100 m
Speed: 10+ kt submerged, 6+ knots surfaced
Operating depth: 1,000m (3,300ft)
Power plant: 2 x 400 kW generators driving 1 x 300 kW electric motor
Crew: 10 + 10 PAX
Endurance: 21 days
Armament: 2 x 533mm (21") heavyweight torpedoes
Payload: 2 x 4 PAX swimmer delivery vehicles (SDVs)

Significantly this design is a private project for Larsen & Toubro (L&T). While the layout does bear some resemblance to the Italian Cos.Mo.S / Drass X-craft, it is an original design. And its market appears to be for export rather than local use although the Indian Navy has for many years had an interest in midget submarines.

The project is not the first small submarine design from L&T. They are also involved the design of a coastal submarine with the Indian Navy. Although the two designs are similar, it is unclear of the exact relationship. The other design bears a stronger relationship to the German Type-209 family which is operated by India.