India’s sea-based nuclear deterrent is set to get a major boost with the commissioning of its third indigenously built Arihant-class nuclear-powered ballistic missile submarine (SSBN), INS Aridhaman (S4), likely by April-May, defence sources said.Built under the Advanced Technology Vessel (ATV) project at the Ship Building Centre in Visakhapatnam, INS Aridhaman weighs 7,000 tonnes, making it larger than its predecessors INS Arihant and INS Arighaat (6,000 tonnes).The submarine carries eight vertical launch system (VLS) tubes, compared to four on earlier vessels, allowing it to deploy up to 24 K-15 Sagarika short-range missiles (750 km) and eight K-4 intermediate-range missiles (3,500 km). It can also accommodate K-5 missiles with a range of 6,000 km.INS Aridhaman is powered by an 83 MW Compact Light Water Reactor (CLWR), an upgraded pressurised water reactor with a very low acoustic signature. It features a seven-blade propeller, enabling speeds of 12–15 knots on the surface and 24 knots submerged. Advanced indigenous sonar systems USHUS and Panchendriya, along with anechoic tiles, improve stealth and detection capabilities.Once operational, India will have three SSBNs under the Strategic Forces Command, marking a key step towards achieving Continuous At-Sea Deterrence, which ensures at least one nuclear submarine is always on patrol. INS Aridhaman’s enhanced missile payload and stealth will strengthen India’s “second-strike” capability.The submarine will be stationed at Project Varsha, a high-security naval base with underground pens near Visakhapatnam. Meanwhile, India is also set to acquire the Russian Akula-class nuclear-powered attack submarine, Chakra III, expected by 2027–28, and is negotiating with Germany for six advanced diesel-electric submarines under Project-75(I).