Indian Navy to test K-6 hypersonic ballistic missile for future underwater nuclear strike force.

According to IDRW on June 25, 2025, India is moving forward with the development and upcoming testing of the K-6 submarine-launched ballistic missile (SLBM), a new strategic missile system under the Defence Research and Development Organisation (DRDO). The existence of this missile was publicly acknowledged during a panel discussion at the Kerala Spacepark (KSPACE) foundation stone laying ceremony in Thiruvananthapuram.
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The development of the K-6 follows the operationalization of earlier K-series submarine-launched ballistic missiles (SLBMs), such as the K-15 Sagarika, which has a range of 750 to 1,500 kilometers. (Picture source: Indian MoD)

A former BrahMos Aerospace scientist stated that DRDO had already completed development of the K-5 SLBM and that the K-4 missile had entered service with the Indian Navy. The K-6, with a planned range of 8,000 kilometers and a speed of Mach 7.5, is being designed to enhance the sea-based leg of India's nuclear triad. The missile will arm the upcoming S5-class submarines, which are expected to surpass the Arihant-class in terms of size and missile capacity. These developments form part of India’s broader efforts to maintain a credible second-strike capability and support the “no first use” nuclear doctrine.

The K-6 submarine-launched ballistic missile (SLBM) is being developed by DRDO’s Advanced Naval Systems Laboratory (ANSL) in Hyderabad. It is a three-stage, solid-fuel missile that incorporates multiple independently targetable reentry vehicles (MIRVs), which enable it to strike several targets in one launch. The missile exceeds 12 meters in length and over 2 meters in diameter, and it is designed to carry a payload of up to 3 tonnes. Its reported range of approximately 8,000 kilometers allows it to cover most of Asia and large parts of Europe and Africa when launched from secure patrol zones in the Indian Ocean. With a terminal reentry speed of Mach 7.5, equivalent to roughly 9,200 kilometers per hour, the missile reduces adversary response time and makes interception by missile defense systems more difficult. Its high velocity and trajectory characteristics increase the likelihood of penetrating multi-layered defenses and striking targets at intercontinental distances.

The K-6 missile is intended for integration into the S5-class of Indian nuclear-powered ballistic missile submarines, which are planned to have greater displacement and missile capacity than the current Arihant-class. These submarines are expected to displace around 13,500 tonnes and feature between 12 and 16 vertical launch system (VLS) cells capable of launching either K-5 or K-6 missiles. Development of the S5-class began after it was determined that the Arihant-class had limited strike range and payload capacity. The S5 submarines are to be powered by a CLWR-B2 compact light water reactor generating 190 MW and will use a pump-jet propulsion system. Their design phase was nearing completion as of late 2024, and production is expected to start by 2027. These submarines are being developed to allow Indian SSBNs to launch intercontinental-range missiles while remaining in safer maritime regions, thereby reducing the need to operate in contested waters near adversary territories.

The development of the K-6 follows the operationalization of earlier K-series SLBMs. The K-4, with a range of 3,500 kilometers, is deployed aboard INS Arihant and INS Arighaat. This missile is 10 meters in length, weighs 20 tonnes, and carries a 2-tonne payload. It was successfully tested from an underwater platform and from INS Arighaat, including a notable test on November 28, 2024. The K-5, developed between 2015 and 2024, has an estimated range of 5,000 to 6,000 kilometers, includes MIRV capability, and is designed for future Arihant-class variants such as S4 and S4*. While the K-5 is reportedly completed, it has not yet undergone public testing. The earliest K-series missile, the K-15 Sagarika, has a range of 750 to 1,500 kilometers and remains in service aboard the original Arihant-class submarines. These missiles are supported by the Indian Regional Navigation Satellite System (IRNSS), providing enhanced navigation and targeting precision.

The Arihant-class submarines form the current basis of India’s sea-based deterrence. INS Arihant was commissioned in 2016, followed by INS Arighaat in August 2024. Both submarines are operational and capable of carrying either twelve K-15 SLBMs or four K-4 SLBMs. Two additional submarines, designated S4 and S4*, were launched in November 2021 and October 2024, respectively. The S4-class boats are designed to carry up to eight K-4 or K-5 missiles. These platforms have an increased displacement compared to the first two vessels and incorporate a more powerful pressurized water reactor. A fifth unit of the Arihant-class is also in planning. The submarines are equipped with torpedo tubes and carry additional weaponry such as mines or cruise missiles. They use indigenous components, including control systems from Tata Power SED and propulsion elements from Walchandnagar Industries. Testing and training were supported by a land-based prototype reactor at Kalpakkam and the leased Russian INS Chakra Akula-class submarine.

India’s K-series missile program is distinct from its Agni series due to its submarine-launch capability and its reliance on solid-fuel propulsion with advanced composite propellants developed by the High Energy Materials Research Laboratory (HEMRL). These advancements enable reduced weight and increased speed without sacrificing range. The K-series missiles are built to be more compact and efficient for submarine integration, with increased stealth and survivability characteristics. The K-6, in particular, adds flexibility by being capable of carrying either nuclear or conventional warheads. According to reports, it may carry 4 to 6 MIRVs depending on payload configurations. These features make the K-6 suitable for both deterrence missions and potential conventional strategic roles, depending on geopolitical circumstances. The missile’s development has reportedly continued under strict confidentiality, consistent with India’s policy of minimal public disclosure on strategic programs.

India’s missile programs aim to support the operationalization of its nuclear triad, which consists of land-based Agni missiles, air-delivered nuclear bombs, and submarine-launched ballistic missiles. The introduction of the K-6 SLBM and the future S5-class submarines is intended to ensure that the sea-based component of the triad becomes more robust and less vulnerable to preemptive strikes. This development is considered necessary in light of regional developments, particularly China’s deployment of Type 096 submarines with JL-3 SLBMs, which have reported ranges exceeding 10,000 kilometers. The integration of the K-6 would address India’s current limitations in engaging distant targets from secure maritime locations. With the K-6 and S5-class programs, India aligns its deterrence posture with that of the five established nuclear powers, the United States, Russia, China, France, and the United Kingdom, which all possess or are developing comparable submarine-launched MIRV-capable intercontinental ballistic missiles. India’s strategic trajectory now places increasing emphasis on undersea capabilities for ensuring credible retaliatory options in any escalation scenario.