India tests K-4 Long-Range Nuclear Missile from newly commissioned INS Arighaat submarine

By R Anil Kumar

Bengaluru, December 27, 2025. India has test-fired the K-4 intermediate-range submarine-launched ballistic missile from the nuclear-powered submarine INS Arighaat in the Bay of Bengal. The launch strengthens the survivability of India’s nuclear deterrent and signals growing confidence in its sea-based second strike capability.

India has conducted a test launch of its K-4 submarine-launched ballistic missile from the nuclear-powered ballistic missile submarine INS Arighaat, marking what Indian sources describe as the first time the missile has been fired from that platform. The test took place in the Bay of Bengal off the coast of Visakhapatnam on December 25, 2025, with no immediate public confirmation from the Ministry of Defence. Defense analysts view the launch as a meaningful step toward operationalizing the sea-based leg of India’s nuclear posture.

The K-4 submarine-launched ballistic missile is a solid-fuel, two-stage nuclear-capable weapon with a range of around 3,500 km, designed to be fired from Arihant-class submarines, allowing India to conduct survivable second-strike nuclear deterrence patrols far from adversary coastlines.

K-4 represents a different category of undersea strike tool than India’s earlier K-15. K-4 is described as a solid fuel, two-stage ballistic missile designed for a 3,500 km class reach and able to carry a nuclear payload of roughly two tonnes. In practical operational terms, a two-stage solid motor stack is well-suited to submarine basing because it is storable, responsive, and compatible with vertical launch systems where crews require minimal exposure and rapid firing timelines. Within the Arihant class design logic, each missile tube can carry multiple shorter-range K-15 missiles or a single larger K-4, making K-4 the range-extending option that prioritizes strategic depth over salvo volume.

That extended range marks a decisive tactical shift. The K-15, with a range of 700 to 750 km, forces Indian ballistic missile submarines to operate closer to adversary coastlines to hold strategic targets at risk. Such proximity increases vulnerability to hostile anti-submarine warfare networks. A 3,500 km class SLBM dramatically enlarges the safe patrol zones available to Indian SSBNs, allowing deterrent patrols in waters where India can more realistically protect maritime patrol aircraft, surface escorts, and emerging undersea surveillance capabilities. From a deterrence standpoint, this directly improves confidence that at least one retaliatory asset would survive a first strike and remain capable of executing national command authority orders.

The platform itself is central to this development. INS Arighaat was commissioned on August 29, 2024, and was officially described as a major reinforcement of India’s nuclear triad. Compared to the lead boat Arihant, Arighaat incorporates design refinements and reflects deeper indigenous industrial integration. The submarine operates under the Strategic Forces Command, underscoring that it is a national strategic asset rather than a purely naval capability.

K-4 also rebalances India’s overall nuclear delivery architecture. The country already fields strong land and air legs, including Agni series intercontinental ballistic missiles with ranges exceeding 5,000 km and nuclear-capable aircraft such as Rafale, Su-30MKI, and Mirage 2000. However, survivability remains the decisive factor in nuclear deterrence. Submarines provide the most resilient leg of the triad, especially under India’s declared doctrine of credible minimum deterrence and No First Use, which reserves nuclear weapons solely for retaliation designed to inflict unacceptable damage.

India’s continued investment in sea-based deterrence is shaped by its regional security environment. The country faces two nuclear-armed neighbors and recurrent crisis dynamics in South Asia, where escalation risks remain a constant strategic concern. Even limited conventional confrontations routinely trigger international anxiety over potential nuclear dimensions. Against this backdrop, India consistently argues that restraint and No First Use must be underpinned by survivable retaliatory forces to deter coercion or miscalculation.

The K-4 test also fits into a longer-term force development trajectory. India plans additional ballistic missile submarines, including INS Aridhaman, expected to enter service in the near future, alongside follow-on boats with greater endurance and missile capacity. Parallel development of longer-range K series missiles such as K-5 and K-6 further indicates an ambition to ensure sea-based deterrence remains credible against evolving threats. The significance of the K-4 launch lies not in a single test, but in how it transforms the Arihant class into a more survivable, strategically flexible second strike force aligned with India’s doctrine and long-term security calculations.