India tests K-4 ballistic missile from nuclear submarine INS Arighaat

India has reportedly tested an intermediate-range ballistic missile that was launched from the nuclear-powered submarine INS Arighaat. The test of the K-4 missile, according to media reports, took place in the Bay of Bengal, off the coast of Vishakhapatnam, on Tuesday (December 23).

With a range of 3,500 kms, the K-4 missile provides a major boost to India’s naval nuclear deterrence. The submarine-launched ballistic missile was commissioned by the Indian Navy on August 29, 2024, catapulting India into an elite club of nations with the capability of launching a nuclear missile from land, air, and undersea.

K-4 derived from Agni-III

The K-4 missile has been derived from the Agni-III land-launched missile, reported by NDTV, adding that the land version of the missile has been modified for sea launch and has the ability to pop out of a submarine launch silo, bubble up to the ocean surface, and then start its rocket motor.

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The report further stated that the intermediate-range K-4 missile can deliver a 2.5-ton nuclear warhead and can be launched from India's Arihant-class submarines.

The 'K' in the K-series of missiles is a homage to APJ Abdul Kalam, who played a crucial role in India's Integrated Guided Missile Development Program (IGMDP).

The submarine that launched K-4

INS Arighaat, the country’s second nuclear-powered submarine armed with nuclear-tipped ballistic missiles, known in naval parlance as an SSBN, was commissioned on August 29 last year.

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Its predecessor, INS Arihant, which became fully operational in 2018, is capable of carrying only the 750-km range K-15 missiles.

India plans to commission its third SSBN as INS Aridhaman in the first quarter of 2026, followed by a fourth submarine in 2027-28 under the secretive Advanced Technology Vessel (ATV) programme, launched decades ago at a cost of over Rs 90,000 crore, reported the Times of India.

India’s plans for larger SSBNs

The third and fourth SSBNs are slightly larger than the first two, with a displacement of around 7,000 tonnes each, compared to 6,000 tonnes for Arihant and Arighaat. There are also plans to eventually build much larger 13,500-tonne SSBNs, equipped with more powerful 190 MW pressurised light-water reactors, replacing the existing 83 MW reactors fitted on the first four submarines.

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India’s current SSBNs remain less than half the size of those operated by the United States, China and Russia. However, the operational deployment of K-4 missiles, to be followed by the K-5 and K-6 missiles in the 5,000–6,000 km range class, is expected to help India narrow the capability gap with countries that possess a large inventory of intercontinental ballistic missiles, stated the report.

India’s nuclear triad

The first two legs of India’s nuclear triad are considered more robust, with land-based ballistic missiles led by the Agni-5, which has a strike range of over 5,000 km, and fighter aircraft such as the Rafale, Sukhoi-30MKI and Mirage-2000, all capable of delivering nuclear gravity bombs.

The SSBNs, however, lend India’s deterrence posture greater credibility, as they are widely regarded as the most secure, survivable and potent platforms for retaliatory strikes, in line with the country’s stated “no first-use” nuclear policy.