India completes development of K-5 nuclear ballistic missile to expand submarine strike range.

According to IDRW on June 25, 2025, India’s Defence Research and Development Organisation (DRDO) has completed development of the K-5 submarine-launched ballistic missile (SLBM), a nuclear-capable system with an operational range of 5,000 to 6,000 kilometers. This confirmation was made during the foundation stone laying ceremony of the Kerala Spacepark (KSPACE) in Thiruvananthapuram, where a former BrahMos Aerospace scientist also stated that the K-4 SLBM (3,500 km range) has been inducted into service aboard Arihant-class submarines.
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India has completed the development of the K-5 nuclear ballistic missile with a range of 5,000 to 6,000 kilometers, while the shorter-range K-4 missile, capable of reaching up to 3,500 kilometers, has already been inducted into service aboard Arihant-class nuclear-powered submarines. (Picture source: DRDO)

He further noted that the DRDO is actively developing the K-6 SLBM, which is expected to have a range of up to 8,000 kilometers and achieve speeds of Mach 7.5. These updates were disclosed during a panel discussion on indigenous defense technologies attended by government officials, industry leaders, and scientists. The KSPACE facility itself is designed to support aerospace and defense innovation and facilitate collaboration among research institutions, startups, and private sector entities.

The K-5 missile program was launched in 2015 as part of the secretive K-series program intended to develop submarine-launched ballistic missiles (SLBMs) tailored to the Indian Navy’s nuclear-powered submarines. According to information released through multiple Indian defense sources and government-linked media outlets, the missile is a three-stage, solid-fueled system weighing approximately 20 tonnes and capable of delivering a nuclear payload of up to 2 tonnes. The missile has been developed to be comparable in range to the land-based Agni-V intercontinental ballistic missile and incorporates countermeasures to avoid radar detection. It is also reportedly equipped with Multiple Independently Targetable Reentry Vehicles (MIRVs), allowing it to strike multiple targets or increase effectiveness against hardened targets. Earlier reports had indicated that the missile would be tested from a submerged pontoon launcher in the Bay of Bengal, off the coast of Visakhapatnam, in a compressed-range configuration to validate new subsystems prior to full-range trials.

The K-5 is designed for integration with the larger S4 and S4* variants of India’s Arihant-class SSBNs. These submarines feature an increased displacement of 7,000 tonnes and extended hull sections to accommodate eight missile launch tubes. This configuration allows them to carry either eight K-4 or K-5 SLBMs, or up to twenty-four shorter-range K-15 SLBMs, also known as B-05 or Sagarika missiles, which have a range between 750 and 1,500 kilometers. The lead vessel of the Arihant class, INS Arihant, was commissioned in 2016 and can carry four K-4 missiles or twelve K-15 missiles. The second unit, INS Arighaat, was launched in 2017 and formally commissioned in August 2024 following prolonged sea trials. S4 was launched in 2021 and is undergoing final trials with expected commissioning in 2025. S4* was launched in October 2024. A fifth Arihant-class submarine, the third of the S4 subclass, has been approved for construction. These SSBNs are equipped with an 83 MW pressurized water reactor developed by BARC, USHUS sonar systems, and indigenous combat control systems.

DRDO has publicly showcased several K-5 components, including its canister, nose cap, torrential air bottles, and the TOR gas generator casing. The missile is cold-launched using gas pressure from its canister before its rocket motors ignite, which reduces acoustic and thermal signatures and improves stealth characteristics underwater. The nose cap protects the payload during underwater ejection and detaches once the missile exits the water column. With a length of approximately 12 meters and a diameter of 2.45 meters, the K-5 shares design similarities with the Russian R-39 SLBM. It is optimized for deployment in the deep-sea bastions of the Bay of Bengal, where India’s continental shelf drops sharply, allowing SSBNs to submerge close to port and remain concealed. With its long range and MIRV capability, the K-5 is intended to enable SSBNs to strike targets across all of China and significant portions of Asia and Europe from secure waters near Indian territory, without requiring forward deployment.

The development of the K-series is part of India’s broader effort to establish a layered and survivable second-strike nuclear posture. The K-series includes the K-15 (750–1,500 km), K-4 (3,500–4,000 km), K-5 (5,000–6,000 km), and K-6 (6,000–8,000 km) SLBMs. These systems are reported to be lighter and more compact than the Agni missile family due to advances in propellant chemistry and composite materials developed by DRDO’s High Energy Materials Research Laboratory (HEMRL). The K-5 was initially expected to be tested by 2022, and its completion aligns with the phased buildup of India's sea-based nuclear force. The K-6 is currently under development at DRDO's Advanced Naval Systems Laboratory in Hyderabad. It will reportedly be a three-stage solid-fueled SLBM capable of delivering a 2–3 tonne MIRV payload over distances exceeding 8,000 kilometers. It is planned for deployment aboard the S-5 class SSBNs, which will displace approximately 13,500 tonnes and carry twelve SLBMs.

India's SSBN program is being executed under the ₹900 billion Advanced Technology Vessel (ATV) project. This program is supported by a national industrial and research ecosystem spanning multiple states and agencies, including BARC, DRDO, the Indian Navy, Larsen & Toubro, Tata Power SED, and Walchandnagar Industries. INS Arihant's onboard nuclear reactor became critical in August 2013, and the vessel began sea trials in December 2014. The submarine completed its first deterrent patrol in 2018, making India the sixth country to operate a ballistic missile submarine. In addition to the SSBN fleet, India has committed to constructing six nuclear-powered attack submarines (SSNs), for which the design work is being conducted at a dedicated submarine design center in Gurgaon. These submarines are expected to be armed with cruise missiles and torpedoes and have greater mobility compared to SSBNs.

India's current fleet consists of one operational SSBN, INS Arihant, with INS Arighaat recently commissioned and S4 and S4* undergoing trials. The country also operates 17 diesel-electric attack submarines of the Sindhughosh, Shishumar, and Kalvari classes. India has leased Akula-class SSNs from Russia for training and operational familiarization and is expected to receive a new SSN from Russia to replace the returning INS Chakra. India has constructed strategic naval bases, including INS Varsha, a concealed submarine base near Rambilli on the east coast, designed to accommodate its expanding SSBN and SSN fleets. This site allows rapid access to deep waters, where ballistic missile submarines can dive and remain undetected.

The K-5 SLBM enhances India’s nuclear triad by providing a survivable second-strike capability at sea. This deterrent is structured under India's nuclear doctrine, which emphasizes credible minimum deterrence and a strict no-first-use policy. Sea-based deterrents are considered the most secure and least vulnerable to a first strike, as SSBNs can remain submerged and undetected for extended durations. The integration of K-5 with newer Arihant-class boats and the planned S-5 submarines reflects India’s objective of maintaining continuous at-sea deterrence. The development of multiple SLBM ranges allows overlapping coverage against strategic targets in China and Pakistan, with launch areas confined to protected maritime zones.

India’s nuclear posture includes land-based Agni series missiles, air-launched weapons, and submarine-launched ballistic missiles. The land-based leg includes the Agni-V, which recently tested MIRV capability, and the tactical Pralay SRBM. The air leg includes modified fighter aircraft, though details remain classified. The underwater leg is centered on the Arihant-class and its successors, and is regarded as the most secure element of the triad. DRDO’s work on the K-5 SLBM, alongside the anticipated K-6, provides India with the ability to hold at risk key adversary targets from secure underwater platforms. The continuous investment in platforms like S-4*, S-5, and future nuclear propulsion systems indicates a sustained trajectory toward strengthening India’s deterrent posture.

The completion of K-5 development also coincides with increased Chinese naval deployments in the Indian Ocean Region (IOR) and continued modernization of Pakistan’s submarine fleet, including the acquisition of Chinese Type 039B attack submarines. These developments are viewed by Indian defense analysts as contributing factors in accelerating sea-based nuclear force enhancements. India’s ongoing SLBM programs, combined with the expansion of its SSBN fleet, aim to establish a secure, credible second-strike capability that remains functional even under the possibility of a nuclear first strike on land-based assets. With the operationalization of the K-5 and the future induction of K-6, India is expected to maintain a posture of assured retaliation with platforms based in waters under its control.