K-4 Ballistic Missile Test by India | UPSC

On December 23, 2025, India successfully test-fired the K-4 submarine-launched ballistic missile (SLBM) from INS Arighaat in the Bay of Bengal, marking a significant milestone in the nation's strategic defence capabilities.

• High relevance for Prelims & Current Affairs
• GS Paper II: International Relations (Strategic balance of power, Nuclear doctrine)
• GS Paper III: Science & Technology (Indigenisation of defence, DRDO achievements) & Internal Security
• Ethics Paper (GS IV): Ethics of deterrence, 'No First Use' policy, responsible statecraft
• Essay Paper: National security, Atmanirbhar Bharat (Self-reliance), geopolitical dynamics

The K-4, also called the Kalam-4, is a nuclear-capable intermediate-range submarine-launched ballistic missile (SLBM) developed by India's Defence Research and Development Organisation (DRDO) to arm its Arihant-class submarines.

• Part of the ‘K-series’ missiles, named after Dr A.P.J. Abdul Kalam, who guided India's missile development program.
• The range is approximately 3,500 km, covering all of Pakistan and significant portions of China.
• The missile was launched from Arihant-class nuclear submarines (INS Arighaat).
• It can deliver a nuclear warhead weighing 2 to 2.2 tons.

Also read: Samudrayaan Mission: India’s Journey into the Deep Ocean

The K-4 Missile is one of the strongest weapons in India's arsenal, featuring advanced technologies that make it hard to detect and intercept. 

1. Cold Launch Technology:

• The missile is ejected from the submarine's underwater silo using high-pressure gas.
• Its rocket motor ignites only after it breaches the water's surface, protecting the submarine from heat and damage.

2. High Accuracy:

• It uses a Ring Laser Gyro Inertial Navigation System (RLG-INS) supported by GPS/NavIC satellite guidance, ensuring a Circular Error Probability (CEP) of less than 10 meters.

3. Manoeuvrability:

• The missile can perform 3D manoeuvres in flight, making it difficult for the enemy’s Ballistic Missile Defence (BMD) systems to track or intercept it.

4. Propulsion:

• Powered by a two-stage solid rocket motor, which is safer and quicker to launch than liquid-fuelled missiles.

5. Gas Booster Cold Launch System:

• A gas booster pushes the missile out of the submarine without firing the engine, keeping the submarine hidden.
• The main engine starts only after the missile emerges from the water.

Also read: Mission Sudarshan Chakra: India’s Indigenous Air Defence System

An SLBM is a long-range missile launched from underwater. After launch, it follows a curved path and can hit targets thousands of kilometres away.

Types of SLBMs Based on Range

1. Intercontinental SLBMs (>5,500 km)

• US Trident II D5: 7,600 km (with 8 warheads)
• Russia RSM-56 Bulava: 8,300 km
• India K-6: 8,000 km (under development)

2. Intermediate-Range SLBMs (3,000-5,500 km)

• India K-4: 3,500 km (operational)
• India K-5: 5,000-6,000 km (development completed 2025)

3. Medium-Range SLBMs (1,000-3,000 km)

• India K-15 Sagarika: 750 km (operational)

Types of SLBMs Based on Launch Mechanism

1. Cold Launch

• Gas booster ejects missile; engine ignites after surface breach
• Examples: K-4, K-15, Trident II, Bulava
• Minimal submarine damage, rapid launch capability

2. Hot Launch

• The engine ignites inside the launch tube while submerged
• Less common in modern systems
• High heat damage, slower launch rate

Types of SLBMs Based on Warhead Configuration

1. Single Warhead SLBMs

• One nuclear warhead per missile
• Example: India's K-15, K-4 (currently)
• The disadvantage is that one missile = one target

2. MIRV SLBMs (Multiple Independently Targetable Reentry Vehicles)

• Multiple independent warheads striking different targets
  • US Trident II: 8-12 warheads
  • Russia Bulava: 6-10 warheads
  • India K-5: 2-3 warheads (planned)
  • India K-6: 4 warheads (under development)

Also read: Bharat Forecast System: Launch, Objectives & Key Details

Submarine-launched missiles are a crucial component of nuclear deterrence because they are extremely difficult to detect and destroy. Submarines hidden deep in the ocean are almost invisible to enemy radar and satellites.

• Ultimate Survivability: Submarines constantly move underwater, making them nearly impossible for enemies to track or target in a surprise attack.
• Guaranteed Retaliation: They ensure a "Second Strike Capability", even if a nation’s land and air bases are destroyed, its submarines can still launch a counter-attack.
• Supports "No First Use": For countries like India with a "No First Use" policy, these missiles provide the confidence that they can survive a first hit and strike back.
• Safe Launch Zones: Longer-range missiles (like the K-4) allow submarines to launch attacks from safe waters near their own coast, avoiding dangerous enemy waters.
• Psychological Deterrence: The mere presence of a hidden, silent nuclear threat creates a powerful psychological barrier against aggression.

The K-4 missile test strengthens India’s nuclear deterrence by making it credible, survivable and reliable in South Asia and the Indo-Pacific.

• Completes the Nuclear Triad: India can launch nuclear weapons from land, air, and sea, making its deterrence much stronger.
• Ensures Second-Strike Capability: Even if India is attacked first, submarines with K-4 missiles can survive and retaliate.
• Better Than K-15: K-4 has a significantly longer range, enabling submarines to remain safe in Indian waters.
• Made in India: The K-4 is fully developed by the DRDO, strengthening India's strategic self-reliance.
• Balances China: K-4 helps India maintain nuclear balance with China’s submarine forces.

While the K-4 is a massive success, India’s strategic program continues to evolve to match global superpowers.

• Work is underway on the K-5 (5,000 km) and K-6 (6,000+ km) missiles, which will bring true intercontinental range to India's underwater fleet.
• India plans to induct larger S-5 class submarines (13,500 tonnes) capable of carrying more long-range missiles than the current Arihant class.
• Future variants may incorporate Multiple Independently Targetable Reentry Vehicles (MIRV) to defeat enemy missile defences.

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