India's DRDO has scheduled a missile test in the Bay of Bengal from December 17-20, 2025, triggering a massive 2520 km no-fly and no-ship zone.

This NOTAM, active daily from 6 AM to 6 PM IST, dwarfs the October test's 1480 km radius, signalling a longer-range weapon. Civilian aviation and maritime traffic must reroute, with IAF and Navy enforcing the zone for safety amid potential debris scatter.

Likely Test: K-4 SLBM Details

The profile matches the K-4 submarine-launched ballistic missile (SLBM), India's advanced solid-fuelled system derived from the Agni series:

India's K-4 program develops a nuclear-capable submarine-launched ballistic missile (SLBM) to bolster the sea leg of its nuclear triad, addressing limitations of the shorter-range K-15 Sagarika. Led by DRDO's Defence Research and Development Laboratory (DRDL), the solid-fuelled missile draws from Agni-III technology for enhanced survivability and second-strike capability. Development began post-2009 INS Arihant launch to enable credible minimum deterrence.​

Submarine Integration And Status

INS Arihant (commissioned 2016) and INS Arighat (2024) carry 4 K-4s each; S4/S4* boats (2025 onward) double to 8. By mid-2025, K-4 achieved full operational status on Arihant-class SSBNs, with deployments reported post-Arighat trials. The December 17-20, 2025, Bay of Bengal NOTAM (2520-3550 km zone) likely validates further K-4 maturity or user trials.

Strategic Role

K-4 targets China/Pakistan from safe ocean depths, outranging K-15's 750 km for triad completeness. It precedes K-5 (5,000+ km, in trials) and K-6 (8,000 km MIRV) for S5-class SSBNs by 2030s. Production ramps amid indigenous propulsion advances, tying into Project 75(I) and eastern fleet expansion at Visakhapatnam.

Technical Specifications

The K-4 measures 10-12 meters long, 1.3 meters in diameter, and weighs 17-20 tonnes, carrying a 1-2 tonne payload including MIRV warheads. Its range spans 3,000-3,500 km (up to 4,000 km reduced load), guided by inertial navigation with GPS/NavIC augmentation for <10m CEP accuracy. Launched from 20-50m submarine depths, it integrates with Arihant-class vertical launch systems (4 tubes per boat initially).​

Range: 3,500 km, enabling strikes across regional threats from submerged platforms.

Dimensions And Payload: 12m long, 17 tons; nuclear-capable with MIRV tech for multiple independent warheads.

Launch Specs: Fired from 20-30m depths on SSBNs like INS Arihant or Arihant-class successors.

Strategic Role: Bolsters India's sea-based nuclear triad, enhancing second-strike deterrence against adversaries like China or Pakistan.

This test near Visakhapatnam—home to nuclear sub facilities—validates K-4 integration amid Project 75(I) and SSBN expansions.

Why The Expanded 2520 km Zone?

Missile tests require vast safety buffers due to:

Trajectory and Impact: Full-range flights (up to 3500 km) demand coverage for boost-phase ascent, mid-course, and re-entry splashdown in the Bay of Bengal/Andaman Sea.

Debris Risk: Solid-propellant stages jettison unpredictably; MIRV separation adds variables, doubling prior zones.

Precedents: K-4's November 2024 trials used ~2000 km areas; this escalation confirms maturity toward deployment.

Test AspectOctober 2025 (Prior)December 2025 (This)
Radius1,480 km2,520 km
Implied RangeShorter SLBM variantFull 3,500 km K-4
MonitoringNavy/IAFNavy/IAF (Enhanced)

This aligns with India's push for indigenous SLBMs under the Nuclear Command Authority. K-4 equips Arihant-class boats, countering China's Type 096 SSBNs and JL-3 missiles. Success could accelerate K-5 (5000+ km) development, tying into AUKUS dynamics and Quad maritime security. Visakhapatnam's role underscores eastern seaboard focus post-INS Arighat commissioning.

IDN (With Agency Inputs)