India has quietly expanded its nuclear capabilities by launching its fourth indigenously built nuclear-powered ballistic missile submarine (SSBN). The newly launched SSBN, codenamed S-4*, was unveiled on October 16, 2024, under the radar of major global headlines. Amid simmering tensions with neighboring China and a diplomatic dispute with Canada, this strategic move underscores India’s commitment to strengthening its second-strike nuclear capability.
The S-4* launch represents a critical step forward in India’s nuclear deterrence posture. With the capacity to launch nuclear-tipped missiles, the S-4* joins a fleet of submarines that already includes INS Arihant and INS Arighaat. The submarine was launched under the watchful eye of Defense Minister Rajnath Singh, though the event was largely kept under wraps by the Indian government. Instead of issuing a formal statement on the submarine, the government emphasized the minister’s visit to the inauguration of the Very Low-Frequency Naval Station in Telangana, underscoring the secretive nature of the launch.
A Growing Fleet: Strengthening Second-Strike Capabilities
India’s journey into nuclear-powered submarines began in 2009 with the launch of its first indigenous SSBN, INS Arihant, which was formally commissioned in 2016. The fleet expanded when the Indian Navy inducted its second SSBN, INS Arighaat, on August 29, 2024. Looking ahead, the third submarine, INS Aridaman, is expected to be commissioned in 2025. Once operational, the addition of INS Aridaman will complete India’s minimum triad of deterrence, ensuring that its second-strike capability—a crucial component of a robust nuclear posture—is fully realized.
INS Aridaman, like its predecessors, will be armed with K-15 missiles, which have a range of 750 kilometers, but will also carry K-4 submarine-launched ballistic missiles (SLBMs). These K-4 missiles have a range of 3,500 kilometers, significantly extending the reach of India’s nuclear arsenal. While the K-15 missiles can only cover limited targets, particularly in southern Pakistan, the K-4 provides a strategic advantage by allowing the submarine to strike deeper into the heart of adversary territory, including China.
SSBNs in India’s Nuclear Doctrine
India’s doctrine of credible minimum deterrence hinges on its ability to survive a first nuclear strike and respond with devastating force. The addition of SSBNs to the arsenal ensures survivability, as these submarines can remain hidden in the depths of the ocean, offering the highest level of nuclear deterrence. In contrast to land-based missiles and air-launched nuclear weapons, which are more vulnerable to enemy detection and pre-emptive strikes, SSBNs provide a virtually invisible platform for launching retaliatory strikes.
This capability, known as a second-strike nuclear option, is essential for maintaining a stable nuclear balance, particularly in a region with multiple nuclear powers like South Asia. Having at least one SSBN on constant patrol guarantees that even if an adversary were to launch a surprise nuclear attack, India would retain the capacity to respond. For this strategy to be viable, experts argue that at least 3-4 SSBNs are necessary, ensuring that one submarine can be on patrol while others undergo maintenance or return from missions.
The S-4* and its fellow SSBNs play a vital role in fulfilling this requirement. The submarines are powered by nuclear reactors, allowing them to stay submerged for extended periods and remain undetected by enemy forces. Their ballistic missile capabilities, with ranges extending over several thousand kilometers, ensure that India can retaliate effectively from anywhere in the ocean.
Comparison with Regional Rivals: China and Pakistan
India is not the only nuclear power in the region with sea-based deterrence ambitions. China has been steadily enhancing its submarine fleet and is the only other country in the Indian Ocean region with operational SSBNs. Chinese submarines have been spotted on “counter-piracy patrols” off the coast of Africa, but analysts believe these missions serve dual purposes, including testing the efficacy of Chinese nuclear submarines in distant waters.
Although China’s anti-submarine warfare capabilities are still considered nascent, the presence of Chinese SSBNs adds complexity to the strategic environment in the Indian Ocean. India’s decision to invest heavily in SSBNs, including the S-4*, is partly motivated by the need to counterbalance China’s growing naval influence.
More concerning for India, however, is the emerging possibility that Pakistan could also pursue sea-based nuclear deterrence. Reports indicate that Pakistan is exploring the option of arming its under-construction Hangor-class submarines with nuclear-tipped missiles. These submarines, which are being built with Chinese assistance, could potentially serve as platforms for Tactical Nuclear Warheads (TNWs), providing Pakistan with a rudimentary second-strike capability.
Retired senior Pakistani naval officers have spoken publicly about Pakistan’s ambitions to develop sea-based nuclear deterrence, though the specifics remain unclear. While retrofitting Pakistan’s submarines with nuclear reactors seems unlikely, the deployment of nuclear-tipped cruise missiles on these vessels could still pose a significant threat to India’s security.
India’s Focus Shifts to Nuclear Submarines
To address these regional security challenges, the Indian Navy is prioritizing the development of its submarine fleet. The launch of the S-4* SSBN comes shortly after the Indian government green-lit the construction of the country’s first nuclear-powered attack submarines (SSNs). These submarines are designed not just for deterrence, but also for offensive operations, such as hunting enemy submarines and surface ships. The strategic importance of SSNs is so high that India has reportedly put on hold its plans to develop a 65,000-ton Indigenous Aircraft Carrier (IAC)-2 in favor of accelerating the SSN project.
The construction of the S-4 and S-4 SSBNs* builds on the expertise gained from India’s earlier submarines, INS Arihant and INS Aridaman. At approximately 7,000 tonnes, the S-4 is significantly larger than the 6,000-ton INS Arihant, which is powered by an 83 MW pressurized light water reactor using enriched uranium. The additional size allows for the S-4 to carry more ballistic missiles, thereby enhancing its deterrence capabilities. Satellite imagery from 2021 confirmed that the S-4 is part of the larger ‘Arihant-stretch’ variant of SSBNs, offering greater operational range and strike capacity.
India’s Nuclear Submarine Program
India’s SSBN program, known as the Advanced Technology Vessel (ATV) project, has come a long way since its inception in the 1980s. The launch of INS Arihant in 2009 was the culmination of decades of effort, much of it carried out in secret due to the sensitive nature of the project. The ATV program faced numerous challenges, including delays caused by the disintegration of the Soviet Union in 1991, which had been assisting India in the construction of its nuclear submarines.
Vice Admiral Mihir K. Roy, the first head of the ATV project, recalled the difficulties faced during the early years. After the fall of the Soviet Union, contracts had to be renegotiated, and progress stalled as Russia grappled with political and economic upheaval. The project finally regained momentum in 2004 when new contracts were signed, allowing India to push forward with its goal of building a fleet of nuclear-powered submarines.
The success of the ATV project has been attributed to close collaboration between the Defense Research and Development Organization (DRDO), the Department of Atomic Energy (DAE), and India’s public and private sector. Despite the immense challenges, the launch of INS Arihant marked a historic milestone, proving that India was capable of designing and constructing nuclear-powered submarines domestically.
The S-4 SSBN* marks a crucial step in India’s ongoing efforts to bolster its nuclear deterrence. With an eye on both China’s growing naval presence and the potential for Pakistan to develop sea-based nuclear capabilities, India is rapidly expanding its own submarine fleet. The addition of the S-4* to the Navy’s arsenal enhances India’s second-strike capabilities, providing a critical layer of security in an increasingly complex strategic environment.
As the world’s fifth nuclear-armed state with operational SSBNs, India continues to demonstrate its commitment to maintaining a credible and survivable nuclear deterrent. The S-4* is not just a technological achievement; it is a symbol of India’s evolving defense strategy in a region where the balance of power is constantly shifting.
