When INS Arihant, India’s only in-service nuclear submarine (ballistic missile submarine or SSBN) completed its first deterrence patrol in November 2018, the country achieved a significant milestone — operationalisation of the triad, the capability to launch nukes from land, air and sea. However, this was largely symbolic, and one of the reasons behind this is the missile the boat carried.

The Arihant, during the deterrence patrol, was armed with Sagarika K-15 (or B-05) submarine launched ballistic missiles (SLBMs), of which it can carry 12. The K-15 is said to have been operationalised after being “secretly test-fired back-to-back” from INS Arihant in August 2018, just ahead of the deterrence patrol.

For a credible at-sea deterrence, a country’s SSBNs must be capable of, among other things, targeting population and industrial centres of the adversary. In India’s case, this means that the Indian Navy’s SSBNs must be capable of holding at risk cities not only in Pakistan but also in the Chinese mainland.

With the K-15’s 750-km range, targeting Pakistani cities would be possible only from the Arabian Sea, which lowers down the area the Pakistan Navy would have to keep watch over if it was trying to locate an Indian SSBN. This becomes more problematic when one factors in the fact that India has only one SSBN as of now.

Cities in the Chinese mainland would remain outside the range of the missile even if the boat was at the north-eastern edge of the Bay of Bengal. Therefore, in the event of a crisis with Beijing, New Delhi would not have the option of threatening a nuclear attack on a target of consequence in China. (Theoretically, the SSBN can reach closer to China to make up for the short-range of the missile, but it will be at an increased risk of detection or worse — an attack).

Therefore, India may have operationalised its triad, but the naval leg or the at-sea deterrent is not credible given the limited range of the missile it uses.

The next in the K-series of missiles, the intermediate-range K-4, is the solution. The missile was test-fired on Sunday (19 January).

With the 3,500-km range K-4, INS Arihant and future SSBNs will be able to target parts of China, including Beijing, and all of Pakistan, from the northern parts of the Bay of Bengal. Not ideal, but better than the K-15.

This test wasn’t the first launch of the K-4 SLBM. Testing of the missile began in 2010 from a submerged pontoon, and, according to this report in The New Indian Express, it was fired from INS Arihant in 2016 at an undisclosed location in the Bay of Bengal “in full operational configuration”.