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-
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. - |
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. - |
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).
8 comments:
A great post Gessler
I wonder if the power output (thermal) of the CLWR-B1v2 is proportionate to the increase in displacement of S4 (~9,000 tons submerged) over S2 and S3 (both ~8,000 tons submerged). This output may be a 15% increase over S2 and 3's 90MWt. So about 105MW(t) for S4 especially if the Indian Navy desires slightly higher speed.
Here's an interesting post at https://www.reddit.com/r/IndianDefense/comments/11z8b22/nuclear_reactors_of_indian_navy_submarines/
"Recently Alpha Defense published an article on “Nuclear Reactor Revolution” on its website. After reading it, I think there is still lot of things which are not fully covered in that article, so let’s take a deep dive.
let’s examine...“CLWR-B1” PWR built by Bhabha Atomic Research Centre (BARC). CLWR = Compact Light Water Reactor.
The B1 is already used on the Arihant-class SSBNs (INS Arihant, INS Arighat), where it produces about 90MWt (Megawatt Thermal) using 40% High Enriched Uranium (HEU) fuel.
Now this “B1 PWR” is heavily based on the Soviet “VM-4/4SG” [https://en.wikipedia.org/wiki/VM_reactor ] reactor, designed by "NIKIET". This is the same type that powered the Charlie-class SSGN “INS Chakra-1” that India leased between 1988-91. These leases happened for a reason. Namely, to train & certify a full crop of naval engineers on operation of a particular reactor type under project ATV (Advance Technology Vessel), and to understand its characteristics.
The “VM-4/4SG PWR” produces a similar range of power (70-90MWt), with the one large modification being the switch to 40% enriched Uranium by India, as compared to 20% enriched Uranium which the Charlie Class used by Soviets."
India has been wise enough not to totally rely on indigenous developments. Especially in the 1990s Russia and its contractors needed the money. The Ukraine War might be seeing a resumption of Russian need for Indian money.
Next I'll look at Hypersonic missile developments, especially building on your excellent https://gentleseas.blogspot.com/2024/12/k-4-slbm-launch-from-submarine-indian.html
Cheers Pete
Hi Pete,
I thought that the text in the post you quoted was eerily similar to an analysis I did on my Twitter/X account way back in 2021 (based on the best information I had at the time), and sure enough somebody (I'm assuming the post writer himself) pasted a link to my old Twitter thread in the comments under that Reddit post, possibly acknowledging it as the source material: https://www.reddit.com/r/IndianDefense/comments/11z8b22/comment/jdbwmt0/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
The thread in question: https://x.com/Parthu_Potluri/status/1444631861502767109?s=20
In that thread I posited that the CLWR-B1 may have been either based directly on the VM-4 design or at least inspired by it (with the Russians serving to validate the design against their baseline), taking it forward I also speculated that the CLWR-B2 could be derived from the design of the OK-650B (Akula-class reactor), which is something I've said on this blog as well several times. Though it still remains just my opinion.
Cheers
Hi Gessler
Even if just an opinion insights like yours are very valuable and often all we (outside of Russian design bureaus and outside of apparatchiks in large Western military intelligence agencies) have got to go on.
Possibly https://en.wikipedia.org/wiki/S5-class_submarine right sidebar at "1 x CLWR-B2 Compact Light-water reactor[3][4] 200 MW" is drawing from your ideas as well.
Also, it was Charles Caleb Colton in his 1820 work "Lacon: or Many Things in Few Words" who first said "Imitation is the sincerest form of flattery" :)
Regards Pete
I find it interesting that there are no publicity photographs of Indian SSBN's, except for a couple of images of the INS Arihant during its trials. HI Sutton commented about the Arihant's design similarities to the Kilo-class:
https://www.hisutton.com/Vanquisher-20of-20Enemies-20-20INS-20Arihant.html
I reckon that with the injection of submarine technology from the French (Project-75 Kalvari-class) the S5 boats will be markedly different from the S1, perhaps a Scorpene-derived design like the Brazilian S-BR Alvaro Alberto?
Hi Shawn
I also agree with H I at https://www.hisutton.com/Vanquisher-20of-20Enemies-20-20INS-20Arihant.html when he writes Arihant was "Undoubtedly built with some Russian design assistance".
I'd add that India may have done well to encourage Russian assistance with the K series missiles (including Arihant's K-4's) and perhaps even Russian thermonuclear explosion test results.
The latter is similar to the likelihood of Israel working alongside France on A and H bomb tests and designs.
I reckon all nuclear armed countries included some foreign assistance/collaboration or espionage in their programs.
For more see:
Vipin Narang's "Seeking the Bomb: Strategies of Nuclear Proliferation". He analyzes how states acquire nuclear weapons based on their security environment. The book argues that the how—sprinters, hedgers, or sheltered players—is decided by strategic, technical, and political factors.
Cheers Pete
Hi Shawn & Pete,
The lack of many publicly-available images/official graphics is indeed frustrating (especially to those writing about these boats), the brilliant artworks by the likes of H.I. Sutton serve as invaluable stand-ins under these conditions.
As of the Arihant's design, the bow section especially bears more than a passing resemblance to the bow of the Kilo-class. Even the conning tower's shape invokes the Kilo, though the Arihant has its dive planes on the tower itself unlike the Kilo which has them on the hull. The other major differences are obviously the missile hump & the presence of a vertical tailfin/rudder above the screw, which is distinctively lacking on the Kilo. I'm convinced that there's a Russian hand in the design, or at the least serving to validate/certify the designs being proposed by the Indian side.
It probably serves to know that the Arihant-class (pursued under the Advanced Technology Vessel or ATV program) originally started off as a program meant to build SSNs. It was only later that the decision was made to convert the program into an SSBN effort, following the 1998 nuclear tests and subsequent full-fledged weaponization of the nuclear capability that was initially demonstrated back in 1974 but kept in a dormant/non-weaponized state till the late 1990s, when it became clear that Pakistan was on the brink of weaponizing its own. A second-strike capability delivered via SSBN was seriously considered at that point.
Coming to the S5 and a possible French design connection, I personally don't see it happening though I have been wrong before. Chiefly because the Scorpene/Kalvari-class build program, while delivering significant 'know-how' regarding the production-engineering process of modern single-hulled submarines, doesn't really deliver much 'know-why'. If there is to be a foreign hand in providing assistance in the S5 (or even the P77 SSN) program, I'd reckon it would again be Russian.
But we can't rule out the French entirely either, there have been too many visits (just counting the publicly-known ones) of personnel from the Indian Navy & DRDO to French yards and offices involved in the Barracuda/Suffren-class program for it to have been for nothing (see linked tweet).
https://x.com/Parthu_Potluri/status/1875897550252982684?s=20
We'll have to wait & see how the actual boats turn out and whether they bear any resemblance to existing French/Russian designs. There have been at least two distinctly different hydrodynamic design iterations of the S5 that were seen publicly so far (one with a prominent missile hump & dive planes on the hull and the other with a thoroughly streamlined hump and dive planes on the tower), neither of which appear to be directly resembling any existing design.
The SSN on the other hand, we don't know anything about its design yet. Even Sutton's artwork of it is complete conjecture at this point.
My next article that I'll probably publish next week is regarding some new developments in the S5 program (and a subsequent article about its deterrence load, the K-5 SLBM), so stay tuned!
Cheers
Thanks Gessler very interesting. Looking at the overall production rate, after a slow start (understandable given it is India’s first SSN) India is now producing Arihant class SSBNs at the rate of one every two years. That is faster than the build rate UK has achieved on Astute class SSNs (one every three years or more).
Hi Anonymous at 10:36 AM on 5/03/2026
You're welcome. Regarding the size & scope of India's build program, my next article (should appear in a day or two) will have something worth reading. So be sure to check back at the blog!
Post a Comment