Indian successfully tests nuclear capable K-4 sub-ballistic missile in Bay of Bengal | Know why it special

In a significant boost to its strategic defense capabilities, India successfully test-fired the K-4 submarine-launched ballistic missile (SLBM) from the nuclear-powered submarine INS Arighat in the Bay of Bengal on Thursday, December 25, 2025. The missile, which has a striking range of 3,500 kilometers, was launched in full operational configuration. Developed by the Defence Research and Development Organisation (DRDO), the K-4 is designed to carry a nuclear warhead weighing up to two tonnes, making it a formidable component of India's underwater arsenal.

The K-4, often referred to as 'Kalam-4' in honor of Dr. A.P.J. Abdul Kalam, is an intermediate-range missile specifically engineered for Arihant-class submarines. Unlike its predecessor, the K-15, which has a limited range of 750 km, the K-4 allows Indian submarines to maintain a credible second-strike capability from safe distances in the deep ocean. This test is a critical step toward the missile's full operational induction, with technical data now being analyzed to ensure all mission parameters were met.

Technologically, the K-4 stands out for its high accuracy and stealth. Measuring 12 meters in length and weighing nearly 17 tonnes, the missile uses a cold-launch system where it is ejected from the submarine before its solid-fuel rocket motor ignites. It utilizes an advanced navigation system supported by NavIC (India's indigenous GPS) and is capable of performing three-dimensional maneuvers to evade enemy missile defense systems, ensuring it can penetrate sophisticated shields.

This successful trial from INS Arighat, the second submarine of the Arihant class commissioned in late 2024, reinforces the sea-based leg of India’s nuclear triad. The development ensures that India maintains a survivable and potent retaliatory strike option in line with its "No First Use" nuclear doctrine. As India moves toward commissioning its third and fourth nuclear submarines (INS Aridhaman and others), the integration of K-4 missiles marks a coming-of-age for the nation’s undersea strategic deterrence.