Indian Navy 3rd SSBN (S4) is likely to enter sea trials this year
The first of these SSBNs, the INS Arihant (S2), after which the class is named, was launched in July 2009, with sea trials commencing in December 2014 and commissioning into the Indian Navy taking place in August 2016.
The second in the series, S3 or INS Arighat, is in the advanced sea trials phase and is expected to be commissioned soon. The newest submarine is numbered S4 but yet to be named [INS ARIDHAMAN].
The S4 is bigger in size, tonnage, and capability compared to S2 and S3. The S2 and S3, which can carry four K-4 or 12 K-15 Submarine Launched Ballistic Missiles (SLBMs), the S4 is being built to accommodate eight K-4 or 24 K-15 SLBMs
