The K-4 (Kalam-4) is a nuclear-capable, intermediate-range, submarine-launched ballistic missile (SLBM) developed by India’s Defence Research and Development Organisation (DRDO). The K-4 is 10 meters long, weighs 20 tons, and can carry a 2-ton payload. It has a maximum range of about 4,000 kilometers.

The K-4 is part of the K missile family, a series of underwater launched ballistic missiles developed by DRDO and Bharat Dynamics Limited (BDL). The K missile family is named after Indian scientist and former President A.P.J. Abdul Kalam. The K family missiles are faster, lightweight, and stealthier than land-based Agni Missiles.

Here are the key points about the K-4 SLBM:

Purpose And Deployment:

The K-4 is designed to arm the Arihant-class submarines, which are part of India’s strategic nuclear deterrent
It complements the shorter-range K-15 Sagarika missile
The missile has an effective range of approximately 4,000 kilometers (2,500 miles)

Technical Specifications:

Length: Approximately 12 meters (39 feet)
Diameter: 1.3 meters (4.3 feet)
Weight: Nearly 17 tons (19 tons)
Warhead: It can carry a warhead weighing up to 2.5 tons
Propulsion: Powered by 2-Stage solid rocket propellant
Accuracy: The Circular Error Probability (CEP) is much more sophisticated than comparable Chinese missiles
Manoeuvrability: As a countermeasure against ballistic missile defence systems, the K-4 can perform three-dimensional manoeuvres


Development And Testing:

The development of the K-4 was initiated due to challenges in fitting the similarly capable Agni-III missile into the limited 17-meter diameter hull of the INS Arihant submarine

The K-4 achieved comparable range to Agni-III but with a significant length reduction from 17 meters to 12 meters

The gas-booster designed for K-4 was successfully tested from a submerged pontoon in 2010

Agencies Involved:

The High Energy Material Research Laboratory (HEMRL) and the Advanced Centre for Energetic Materials (ACEM) of DRDO played crucial roles in developing the missile’s propulsion systems.

The Naval Systems Group of the Research and Development Establishment (Engineers) developed the launch system for K-4.


The missile has been tested several times earlier as part of developmental trials to validate different parameters, the source said. The missile ejecting from a submerged platform to the surface [sea] is the toughest part.

There are very few countries which have managed to achieve this technological breakthrough. The Circular Error Probability (CEP) is much more sophisticated than Chinese missiles. The CEP determines the accuracy of a missile. The lower the CEP, the more accurate the missile is.

Once inducted, these missiles will be the mainstay of the Arihant class of indigenous ballistic missile nuclear submarines (SSBN) and will give India the stand off capability to launch nuclear weapons submerged in Indian waters. INS Arihant, the first and only operational SSBN, is armed with K-15 Sagarika missiles with a range of 750 km.

This means the submarine has to venture far way from the Indian waters and move closer to the adversary’s coast to launch the missile. The K-4 will do away with that need.

In November 2019, India formally declared its nuclear triad stated in its nuclear doctrine operational after INS Arihant completed its first deterrence patrol which means INS Arihant has begun prowling the deep seas carrying ballistic missiles equipped with nuclear warheads. It was quietly commissioned into service in August 2016 and its induction was not officially acknowledged. It has a displacement of 6,000 tons and is powered by an 83 MW pressurised light-water reactor with enriched uranium.

In summary, the K-4 SLBM enhances India’s maritime nuclear deterrence capability by providing a potent missile system for deployment on its indigenous nuclear-powered submarines.

(With Agency Inputs)