Part 1: Slew of Developments in the Indian Nuclear Submarine Program: Second SSBN Commissioned

A series of considerable developments took place in India's nuclear submarine program over the last few months as I took a break from online activity owing to computer trouble. I've decided to break my write-up into several parts so that information can be provided in smaller bite-size parcels instead of a single, huge post.

Part-1 is going to be about the second ballistic missile submarine of the Arihant-class, known in the parlance of the Advanced Technology Vessel program as "S3".

The S3 boat was commissioned into service on 29 August 2024 under the name INS Arighaat and the pennant SSBN-81 (first-of-class INS Arihant was SSBN-80). Like the Arihant, the new boat also has the same number of vertical-launch tubes for Submarine-Launched Ballistic Missiles (SLBMs) - Four.

The only available image of the INS Arighaat at sea - a hazy photo taken by a civilian at RK Beach near Vizag, India. Image shared on social media by journalist Sandeep Unnithan

However, unlike the Arihant which carries 12 x K-15 short-range (750km with typical payload of ~1 ton) SLBMs triple-packed in each tube, the Arighaat is believed to only carry 4 x of the medium-range K-4 SLBMs (3,500km with ~1 ton payload), one per tube. Though both submarines retain the ability to carry both types of missiles, both of which are understandably meant for nuclear delivery, as per need.

Also unlike the first boat in class, the Arighaat is believed by some informed opinions to incorporate an 'improved' PWR or Pressurized Water Reactor that delivers an uprated thermal output of ~100MWth compared to the 83MWth of the Arihant's reactor. The increased thermal output can translate into a minor but proportionally higher amount of electrical power on tap that can be used for the submarine's various electronic systems.

While no known iteration exists in the nomenclature to differentiate the improved reactor from the Arihant's baseline CLWR-B1, for sake of avoiding confusion I'd go ahead and designate the new reactor as CLWR-B1v2.

One of the Verticle-Launch Tubes of the Arihant-class, seen here in a triple-pack configuration meant for the K-15 SLBM

The development, testing & certification of the uprated PWR configuration would have been the likely reason for the long gap between the commissioning of S2 (Arihant) in 2016 and S3 (Arighaat) only in 2024. Not to mention, any faults or production engineering-related shortcomings that would only be discovered after several years of at-sea operation of the first boat - which was also the first nuclear-powered submarine that was built in India - would have possibly necessitated a revisit to the drawing board to ensure that the second boat would have those issues addressed before it's certified for active service.

Subsequent boats are likely to be commissioned at a faster pace.

In the next part I'll cover another bit of important news - the launch of 'S4*' which is the 4th and supposedly last of the Arihant-class SSBNs.