India successfully test-fired the K-4 submarine-launched ballistic missile from INS Arighaat, the country's second nuclear-powered ballistic missile submarine. The K-4 has a strike range of approximately 3,500 km and can carry nuclear warheads. This test validates the sea-based leg of India's nuclear triad — the ability to launch nuclear weapons from land, air, and sea — reinforcing credible second-strike capability and survivable deterrence against a nuclear first strike.

India's nuclear doctrine rests on 'No First Use' (NFU) and 'credible minimum deterrence.' For NFU to be credible, India must be able to absorb a first strike and still retaliate with unacceptable damage — this requires a survivable second-strike capability. Land-based missiles (Agni series) and aircraft are vulnerable to a disarming first strike. Submarines, being hidden underwater, are the most survivable platform.

The nuclear triad — land, air, sea — is complete only when all three legs are operationally validated. INS Arihant, India's first SSBN (Ship Submersible Ballistic Nuclear), already patrols with K-15 (Sagarika) missiles of ~750 km range. INS Arighaat is the second SSBN, and the K-4 SLBM extends the sea-based reach to ~3,500 km, capable of targeting adversaries deep inland without the submarine surfacing close to hostile coastlines.

The K-4 is developed by DRDO under the Advanced Systems Laboratory. It uses solid fuel and a canisterised launch system for rapid deployment. It bridges the gap between the short-range K-15 and the longer-range K-5/K-6 missiles under development.

For UPSC, the examiner tests: the components of the triad, which platforms carry which missiles, the doctrine behind NFU, and India's strategic deterrence architecture. The Rajnath Singh context (SCO meeting, anti-terrorism messaging) is the news hook, but the static knowledge being tested is India's nuclear posture and submarine programme.