India marked a major advance in its sea-based nuclear deterrent after a successful test of the nuclear-capable K-4 submarine-launched ballistic missile from the INS Arighaat in the Bay of Bengal.

The test was conducted off the coast of Visakhapatnam on Tuesday.

Designed to strike targets up to 3,500 km away, the K-4 missile enhances India’s sea-based nuclear attack capability.

The missile was launched under the operational control of the Strategic Forces Command, defence forces told India Today TV.

The defence ministry has not issued an official statement on the test.

This was the second test of the K-4 missile from the nuclear-poweredINS Arighaat, following the first launch last year, bringing the system closer to full operational readiness.

Developed by the Defence Research and Development Organisation, the solid-fuel K-4 is intended to arm India’s nuclear-powered submarines.

The K-4 submarine-launched ballistic missile was commissioned into the Indian Navy on 29 August, 2024, placing India among a select group of nations capable of launching nuclear missiles from land, air and undersea platforms.

Derived from the Agni-III land-launched ballistic missile, it is India’s longest-range sea-launched strategic weapon.

The land-based version has been modified for submarine launch, enabling it to eject from an underwater launch silo, surface through a bubble system and then ignite its rocket motor to ascend into the air.

Capable of delivering a 2.5-ton nuclear warhead, the K-4 can be deployed from India’s Arihant-class submarines.

It represents the stealthiest leg of India’s nuclear triad, as ballistic missile submarines are designed to operate in undisclosed oceanic regions for extended periods on “deterrence patrols”.

The missile forms part of the K-series of weapons, with the ‘K’ serving as a tribute to APJ Abdul Kalam for his pivotal role in India’s Integrated Guided Missile Development Program.

INS Arighaat, commissioned into the Navy in August 2024, is India’s latest nuclear-powered submarine, displacing around 6,000 tonnes.

Its induction has enhanced India’s strategic deterrence by enabling the carriage of K-4 missiles with a 3,500-km range.

The first indigenous nuclear-powered submarine, INS Arihant, commissioned in 2016, was armed with K-15 missiles that had a more limited range of 750 km.

Earlier tests of the K-4 had been carried out from submersible pontoons, but launches from INS Arighaat mark a crucial step toward full operational deployment.

While countries such as the United States, Russia and China already field submarine-launched ballistic missiles with ranges exceeding 5,000 km, India’s K-4 programme is viewed as a vital component in closing the gap and reinforcing its strategic capabilities.