India’s recent advancements in its submarine fleet, especially with the launch of its fourth nuclear-powered ballistic missile submarine (SSBN), codenamed S4*, underscore its continued efforts to bolster its strategic deterrence capabilities.

Key points:

• India's latest SSBN, the S4*, was launched on October 16, 2024, at the Ship Building Centre (SBC) in Visakhapatnam. 

• This submarine is larger and more advanced than its predecessors, such as INS Arihant (S2), serving as a significant step in India’s nuclear deterrent capability.

• The S4* features considerable indigenous development, with extensive involvement from Indian industries in its construction, demonstrating the growing self-reliance in critical defence technologies.

• India currently operates two SSBNs, INS Arihant (commissioned in 2016) and INS Arighaat (S3), with INS Aridhman (S4) undergoing sea trials. 

• The S4* is expected to have an improved nuclear reactor and is capable of carrying K-4 submarine-launched ballistic missiles (SLBM), which have a range of 3,500 km, compared to INS Arihant’s 750 km range K-15 SLBM.

• The S4* is designed with greater missile-carrying capacity and improved technology. India's nuclear triad, which enables it to launch nuclear weapons from land, air, and sea, was completed with the first deterrence patrol of INS Arihant in 2018.

Strategic Importance:

• The S4* contributes to India’s Credible Minimum Deterrence (CMD) policy. India maintains a No First Use (NFU) stance but reserves the right to retaliate massively if struck by nuclear weapons. 

• The development of SSBNs like the S4* enhances India’s strategic maritime reach, crucial for monitoring the Indo-Pacific region, where growing geopolitical competition demands robust underwater deterrence. 

About SSBNs (Nuclear-powered Ballistic Missile Submarines)

• SSBNs (Nuclear-powered Ballistic Missile Submarines) are crucial components of a nation’s strategic nuclear deterrence.

• SSBNs provide a second-strike capability, ensuring that even if a country’s land-based nuclear weapons are destroyed, it can still retaliate with its submarine-based nuclear missiles.

• Only a few nations possess this highly specialised military asset — United States, Russia, China, the United Kingdom, France, and India. These countries rely on SSBNs for maintaining a credible and survivable nuclear deterrence.

• Since SSBNs are nuclear-powered, they can remain submerged for extended periods, limited only by the availability of food for the crew, crew fatigue, and the need for periodic maintenance. This makes them nearly undetectable and highly survivable in global strategic waters.

• These submarines carry SLBMs equipped with nuclear warheads, capable of striking targets thousands of kilometers away. 

• India’s SSBNs, for example, carry the K-4 SLBM with a range of 3,500 km, providing long-range strike capabilities from a secure underwater platform.

(The author is a trainer for Civil Services aspirants.)