India tested the K-4 submarine-launched ballistic missile from INS Arighaat in the Bay of Bengal on 23 December 2025. The K-4 has a reported strike range of 3,500 km. The development matters for both defence technology and strategic security because a submarine-launched ballistic missile strengthens the sea-based leg of India's nuclear triad. A nuclear triad is understood through land-based missiles, aircraft and submarines; therefore, a sea-based capability means deterrence is not dependent only on land or air delivery systems.
INS Arighaat is the second Arihant-class nuclear-powered ballistic missile submarine and was commissioned into the Indian Navy at Visakhapatnam on 29 August 2024. The Ministry of Defence release described Arighaat as a step that would strengthen India's nuclear triad and enhance nuclear deterrence. The K-4 test fits into that wider strategic context. Nuclear submarines with long-range ballistic missiles make retaliatory capability more survivable. That is why this capability is linked with second-strike deterrence: even after a first attack, a country should retain the ability to respond.
For exam preparation, the topic is useful for both prelims and mains. In prelims, the missile name, type, reported range, launch area and platform can be asked. In mains, it connects with India's strategic autonomy, indigenous defence technology, maritime security and deterrence. For static GK, it should be linked with the nuclear triad, ballistic missiles, submarine-based deterrence and India's defence technology ecosystem.