India has entered the final stretch in the evolution of its undersea nuclear deterrence capability. A former senior BrahMos Aerospace scientist recently disclosed that the Defence Research and Development Organisation (DRDO) has completed development of the K-5 submarine-launched ballistic missile (SLBM), while the earlier K-4 SLBM has already entered operational service aboard India’s nuclear-powered ballistic missile submarines (SSBNs). However, the most significant news came in the form of confirmation that the K-6 missile—a new generation long-range SLBM—is well underway, with capabilities that could significantly enhance India’s second-strike potential.
The K-6 SLBM, being developed by DRDO’s Advanced Naval Systems Laboratory (ANSL) in Hyderabad, is part of India’s broader ambition to secure its nuclear deterrence through a reliable and survivable sea-based arsenal. With an expected range of 8,000 kilometers, the missile is designed to carry multiple independently targetable reentry vehicles (MIRVs) and travel at terminal speeds of Mach 7.5. This next-generation weapon system will be the mainstay of the upcoming S5-class nuclear submarines, providing a formidable leg to India’s strategic nuclear triad.
India’s K-series missile program has matured quietly but steadily over the past two decades. The first in the family, the K-15 “Sagarika”, with a range of 750–1,500 kilometers, was operationalized aboard INS Arihant, India’s first indigenously built SSBN, in 2016. Though modest in range, the K-15 was critical as a technology demonstrator and foundational system.
Then came the K-4, a medium-range SLBM with a reach of 3,500 kilometers, capable of targeting key adversary assets in mainland China from within Indian maritime boundaries. Weighing 20 tonnes and carrying a 2-tonne payload, the K-4 represents India’s first real deterrent-capable sea-launched missile. It was test-fired successfully from underwater platforms and INS Arighaat multiple times, including in a significant test in November 2024.
Now, with the K-5 reportedly complete and awaiting formal public testing, the program’s maturity has culminated in the K-6. This missile, a three-stage solid-fuelled behemoth over 12 meters in length and 2 meters in diameter, is designed for global reach. The use of solid propellant, developed by DRDO’s High Energy Materials Research Laboratory (HEMRL), enables quicker launch times, greater compactness, and reduced weight—vital characteristics for submarine deployment.
The K-6 missile’s capabilities position it as one of the most advanced SLBMs under development in Asia. Its reported range of 8,000 kilometers would allow it to reach targets in China, Europe, Russia, the Middle East, and large parts of Africa, all from secure patrol zones deep in the Indian Ocean. This capacity is critical for India’s no-first-use doctrine, which relies on a credible second-strike posture to deter nuclear aggression.
MIRV capability is a major leap forward. A single K-6 can carry four to six nuclear warheads, each independently targeted, enabling India to strike multiple enemy locations or saturate missile defenses. Its terminal re-entry speed of Mach 7.5—about 9,200 km/h—dramatically shortens enemy reaction time and presents a difficult challenge for existing anti-ballistic missile (ABM) systems, which must detect, track, and intercept warheads traveling at hypersonic speeds.
In effect, the K-6 marks India’s entry into the elite club of MIRVed SLBM powers—a group that includes the United States (Trident D5), Russia (Bulava and Sineva), China (JL-2, JL-3), France (M51), and the United Kingdom (Trident II D5).
The K-6 will arm the S5-class submarines, currently in advanced design stages. Expected to displace around 13,500 tonnes, these SSBNs will be larger and more capable than the 6,000–7,000 tonne Arihant-class. Each S5 is expected to have 12 to 16 vertical launch system (VLS) cells, capable of launching both K-5 and K-6 missiles.
The S5 submarines will use an advanced CLWR-B2 compact light water reactor, generating 190 MW of power and propelling the vessel through a pump-jet propulsion system. This new propulsion method reduces acoustic signatures, enhancing stealth—critical for survivability and credibility in deterrence patrols.
According to sources within the naval establishment, the S5’s design phase was nearing completion by the end of 2024, and production is expected to begin by 2027. Once operational, the S5s will allow Indian SSBNs to strike intercontinental targets from within safer, unchallenged waters, avoiding high-risk deployments into contested zones like the South China Sea or the western Pacific.
India’s nuclear posture is founded on two core principles: “No First Use” (NFU) and “credible minimum deterrence”. The credibility of a second-strike depends heavily on survivability—and that’s precisely where submarine-based deterrence becomes vital.
Land-based missile silos and air-based nuclear delivery systems are vulnerable to preemptive strikes. Submarines, on the other hand, are difficult to detect and can remain hidden for long durations, ensuring assured retaliation. With the K-6 and S5, India will be able to conduct long-range deterrent patrols, mirroring the capabilities of established nuclear powers.
This capability becomes even more important in light of China’s growing undersea arsenal, including the Type 096 SSBNs equipped with JL-3 SLBMs that reportedly have ranges exceeding 10,000 kilometers. In comparison, the K-6 will bridge the gap and help maintain regional strategic parity.
The SLBM program has significantly benefitted from the Make in India initiative. While early projects relied on Russian support, particularly the INS Chakra Akula-class submarine (leased from Russia), India has steadily built a self-reliant ecosystem.
Control systems are developed by Tata Power SED, and key propulsion components are manufactured by Walchandnagar Industries. Testing and training were conducted at a land-based prototype reactor in Kalpakkam, which helped validate technologies before operational deployment. The Indian Regional Navigation Satellite System (IRNSS) further enhances targeting precision and mid-course guidance for K-series missiles.
With these integrated domestic capabilities, India is reducing dependence on foreign technology and building a robust, indigenous defense manufacturing base.
India has maintained strict confidentiality around the K-6 and related platforms. No public tests have yet been announced, and the missile’s existence was only acknowledged recently during a panel discussion at Kerala’s KSPACE foundation ceremony on June 25, 2025, as reported by IDRW.
Such secrecy is in line with India’s doctrine of minimal public disclosure on nuclear strategy—avoiding destabilizing signaling while keeping adversaries uncertain. The strategy also helps India avoid unnecessary arms race rhetoric while still progressing strategically.
India’s evolving undersea deterrent has multiple geopolitical implications:
- South Asia Stability: The K-6 bolsters deterrence against Pakistan, which lacks a comparable SSBN or SLBM system. The gap may force Pakistan to rely more heavily on tactical nuclear weapons—raising escalation risks in crisis scenarios.
- China Equation: The ability to strike deep into Chinese territory from the Indian Ocean enhances strategic leverage. It deters China from considering counterforce strikes in a hypothetical conflict and limits its coercive options.
- Global Recognition: The K-6 and S5-class represent India’s aspiration to be recognized as a responsible nuclear power with global reach, aligning with its membership in groups like the Missile Technology Control Regime (MTCR) and its bid for a seat at the Nuclear Suppliers Group (NSG).
Despite impressive progress, significant challenges remain:
- Submarine Production: Building SSBNs is resource- and time-intensive. Delays in S5-class production could hamper the timeline for K-6 deployment.
- Command and Control: Effective deterrence requires robust nuclear command, control, and communications (NC3) infrastructure, especially for SSBNs on long patrols.
- Strategic Communication: Balancing secrecy with deterrence signaling is a delicate task. India must ensure adversaries perceive the threat without provoking unnecessary escalation.
India’s K-series missile program, and particularly the K-6 SLBM, underscores its progress toward a fully operational, survivable, and credible nuclear triad. With the integration of MIRV technology, intercontinental reach, and stealthy submarine platforms, India is no longer a regional power playing catch-up—it is shaping into a global strategic force with indigenous capabilities.
