Context: India launched its fourth nuclear-powered ballistic missile submarine (SSBN) at the Ship Building Center (SBC) in Visakhapatnam, enhancing its nuclear deterrence capabilities. This launch follows the commissioning of the second SSBN, INS Arighat in August 2024. The third SSBN, INS Aridhaman, is slated for commissioning next year.

About S4* 

• S4* (codename) is the fourth nuclear-powered ballistic missile submarine (SSBN)

• Naming: India’s first leased nuclear attack submarine INS Chakra was named as S1, INS Arihant was named S2, INS Arighaat S3, INS Aridhaman S4 and hence the newly launched one is the last of its class, S4* with the formal name yet to be given.

• The newly launched S4* submarine boasts nearly 75 per cent indigenous content and is equipped with K-4 ballistic missiles, which have a range of 3,500 km and are fired through vertical launching systems.

• While the first SSBN, INS Arihant, carries K-15 nuclear missiles with a range of 750 km, the successors, including S4*, are equipped exclusively with K-4 missiles.

• These submarines have virtually unlimited range and endurance, with operational limits being defined only by food supplies, crew fatigue, and maintenance needs.

Nuclear Submarine

• India's nuclear submarines are advanced naval vessels powered by nuclear reactors, enabling them to operate underwater for extended periods without the need to surface frequently.

• Nuclear-powered submarines are of three kinds.

1. SSN: The one that carries conventional weapons is called an SSN.  

2. SSGN: The second type is capable of carrying guided missiles with conventional warheads.

3. SSBN: The third, and typically the largest and most complex, is the one that is capable of carrying ballistic missiles that may be nuclear armed — an SSBN.

• The SSBN can remain under water for months, and their range limitation is only due to logistics, supplies and crew changes.

India’s SSBN:

• INS Chakra (S1): It was India’s first leased nuclear attack submarine.

• INS Arihant (S2): India launched its first indigenous SSBN in 2009 and commissioned it in 2016.

• INS Arighaat (S3): This year, the Indian Navy inducted its second SSBN, INS Arighaat in August 2024.

• INS Aridhaman (S4): The third submarine, INS Aridhaman, is expected to be commissioned in 2025.

• INS Arihant and INS Arighat are already on deep-sea patrols, and India is set to receive a Russian Akula-class nuclear-powered attack submarine on lease by 2028.

• In parallel, the sixth diesel-electric Kalvari-class submarine, INS Vagsheer, is expected to be commissioned in December this year.

• India’s SSBNs are critical to its strategy against adversaries like China, as aircraft carriers are increasingly vulnerable to Chinese long-range missiles such as the Dong Feng-21 and Dong Feng-26.

India’s nuclear policy

• India’s policy is to have ‘Credible Minimum Deterrence’ (CMD) that underpins its ‘No First Use’ commitment.

• In 1998, India conducted nuclear tests under Phokran-II, and in 2003, India declared its nuclear doctrine based on CMD and a NFU policy while reserving the right of massive retaliation if struck with nuclear weapons first.