India Commissions 3rd SSBN 'INS Aridhaman'

On 4 April 2026, the Times of India reported that Defence Minister Rajnath Singh, alongside Chief of Naval Staff Admiral Dinesh K. Tripathi, had attended the commissioning ceremony of INS Aridhaman, which is the third of the Indian Navy’s Arihant-class nuclear-powered ballistic missile submarines (SSBNs).

In keeping with the tight lid on press releases regarding the SSBN program, not a single image has so far made it to the press from the event itself.

Annotated 3D model of an Arihant Stretch-class SSBN. Sourced via Reddit.
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As written on SubMatts earlier, the INS Aridhaman, also known by its hull number ‘S4’ (and presumed pennant number SSBN-82) is the first of the ‘Arihant Stretch’ sub-class, which has 8 missile launch-tubes and is estimated to be about 130 meters long as opposed to the first two boats which were about 110 meters long and only had 4 missile tubes. The displacement figures are also estimated to have gone up from about 6,000 tons surfaced (possibly ~8,000 tons submerged) to around 7,000 tons surfaced (and ~9,000 tons submerged) on the Stretch.

While the S4 boat, just like the previous two, retains the flexibility to carry either a single K-4 intermediate-range submarine-launched ballistic missile (SLBM) per launch tube or up to 3 x K-15 short-range SLBMs in a triple-packed configuration in each tube (for a total of either 8 x K-4s or up to 24 x K-15s, or any combination in between), it is my opinion that both S3 and S4 would only carry the K-4 SLBMs, due to reasons I mentioned in a previous article of mine.

The Fourth (and presumed last) boat, only known so far by its hull number ‘S4*’ (pronounced S4 Star) and widely anticipated to be named INS Arisudan, is also a ‘Stretched’ boat.

Comparison of Arihant & Arihant Stretch sub-class. Artwork by H.I. Sutton of Covert Shores.
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I had previously written about the launch ceremony of the S4* which had happened in October 2024. I had speculated then, based on reasoning mentioned within that article, that the Fourth boat could be commissioned by 2028 or thereabout, which would then mark the end of the Arihant-class build program.

It is widely believed that every Arihant/Arihant Stretch-class boat since the S3 (INS Arighaat) has an 'improved' Pressurized Water Reactor or PWR, which I had designated as the 'CLWR-B1v2' in the absence of any official literature on what the improved variant should be called. It's not known for sure as to what all went into the improved reactor and how it differs from the base variant that powered the first-of-class INS Arihant (hull S2).