The K-4, developed by India’s Defence Research and Development Organisation (DRDO) with a range capability of 3,500 km, will be an intermediate-range submarine-launched ballistic missile (SLBM). The K-4 arms India’s first indigenously-Ship Submersible Ballistic Nuclear (SSBN) the INS Arihant class submarines, completing India’s nuclear triad of delivery vehicles.
DRDO in April 2019 had test-fired the K-4 nuclear-capable submarine-launched ballistic missile (SLBM)–from aboard the INS Arihant, the first submarine in its class. According to press reports, the test was “highly successful & a roaring success” and involved a fully operationally configured K-4 with a dummy payload. Notably, the K-4 was tested using depressed trajectories.
The K-4 aboard the INS Arihant and future Indian SSBN’s will give India the ability to target most of China, including Beijing, and all of Pakistan when operating in the northern parts of the Bay of Bengal.
While technical details are hard to ascertain given the levels of secrecy involved, the K-4, which underwent its last test on 19th Jan 2020, reportedly has a length of 12 metres, a diameter of 0.8 metres, and can carry a conventional/nuclear payload of up to 2 tons.
The missile is powered by solid rocket boosters and is highly accurate with a near-zero circular error probability.
The INS Arihant will have the capability to carry four K-4 missiles, and the follow-on SSBN’s that are planned will have the capacity to carry eight K-4 or such SLBM’s each. Future submarines will reportedly be larger and will carry missiles of longer range like the S-5, which will have a reach of over 5,000 kilometres.
India has an officially adopted posture of no first use and assured retaliation.
Hence, India considered it essential to develop capabilities to eventually deploy continuous at-sea nuclear deterrence to ensure the survivability of its nuclear second-strike capability. DRDO officials in the past have stated that the circular error probable (CEP) of the K-4 to be 40 meters or less, which would make it an ideal weapon system for a sea-based counter-force capability from stand-off ranges.
In theory, a sea-based nuclear deterrent is invulnerable once undersea because it can hide and is not trackable or targetable by adversaries, unlike ground-based systems.