On the 9th of October 2024, The Cabinet Committee on Security (CCS), the apex decision-making body of the Indian Government regarding all military matters, had officially granted its final seal of approval to the Indian Navy’s nuclear-powered attack submarine program, now designated as Project-77 (previously known as Project-75A).
A sum of Rs. 40,000 crores (equivalent to about US$4.8 Billion) has been allocated toward the construction and acquisition of the first two boats out of a planned total of six – the last four of which are yet to be funded.
Broken into several sections covering everything from propulsion to weapons, the following write-up attempts to provide an in-depth overview of the P77 SSN program with all the information publicly available up to this point, along with several inferences drawn from information regarding other, related programs that might influence the P77’s development or final configuration.
Power & Propulsion
Veteran journalist Sandeep Unnithan who has reported on the Indian nuclear submarine program for over a decade has stated that the P77-class SSNs would incorporate a 190MWth (megawatt-thermal) reactor which would represent a generational leap over the 83-100MWth Pressurized Water Reactors (PWRs) of the Arihant-class. Sandeep Unnithan can be safely assumed as having reliable sources inside the program. Of note is the fact that Mr. Unnithan (then working for the India Today magazine & news channel) was the first journalist who reported that the 3rd and 4th Arihant-class boats will be larger than the first two, years before the ‘S4’ boat – notionally referred to as the Arihant Stretch – first appeared in public in the form of satellite images in late 2021, vindicating his reports.
The new 190MWth PWR, known as CLWR-B2 (CLWR standing for Compact Light Water Reactor) is likely based on or at least built along the same lines as the Russian OK-650B PWR that powers the Improved Akula-class (Project 971I) SSN that India took on lease between 2012-2021 (another boat of this class is now expected to come by 2028, allowing several more Indian crews & naval nuclear engineers to gain at-sea operating experience on the OK-650B). It would also be prudent to infer that the CLWR-B1 that powers the Arihant-class was likely derived from the VM-4 reactor family that powered the Charlie-class (Project 670) SSGN that India leased between 1988-1991. However, any help or guidance from Russian agencies (whether in design itself or at least in the design-validation phase) is unlikely to ever be publicized by either side due to obvious reasons, such as eliciting nuclear proliferation concerns.
On both these reactors, it’s likely that a great deal of redesign and redevelopment was required (with significant involvement of the Bhabha Atomic Research Centre or BARC) in order to bring them up to modern standards of the time – as well as getting them to work optimally in the warm-water conditions of the Indian Ocean Region as opposed to the freezing waters of Russia’s usual operating environments. They’re still likely to use the same level of reactor fuel enrichment as most Russian marine PWRs (~45% enriched HEU). However, I think it can be safe to assume that the new reactor will differ from its baseline Russian design (presumed by me to be OK-650B) to a significantly greater degree than the Arihant reactor’s difference from the VM-4.
While the exact status of the CLWR-B2 program is not publicly known, looking back at this Founder’s Day publication from BARC – the nodal agency responsible for India’s marine PWR program – indicates that a land-based prototype of the B2 reactor may have either been under construction, or even limited operation, as of 2018. The relevant paragraph is pictured below.
The first B2 example was perhaps set up alongside the B1’s land-based prototype at the same facility where the latter is situated in Kalpakkam, Tamil Nadu. Corresponding test & operation simulators of both reactors may also be present at SBC Vizag for shipbuilder’s reference. It’s probably this infrastructure that was supplied by BARC as reported in the above publication.
With around ~60MWe (megawatt-electric) of total electrical power on tap (assuming a ~33% efficiency on a 190MWth thermal output), the P77 SSN would be well-placed to incorporate the 35MW Nuclear-Electric Propulsion (NEP) setup known to have been in the works for the Indian Navy (see image below). Also known as Turbo-Electric Drive in certain navies, this would involve a silent electric motor replacing the noisy reduction gearing used in older submarines. Assuming this setup is indeed intended for application on the SSN project, it can be a reason as to why a significantly higher degree of redesign may have been necessary for the CLWR-B2’s power delivery system – especially the secondary loop setup – as the OK-650B was not originally meant to work with NEP.
For comparison, the French Navy’s Barracuda/Suffren-class SSN uses a 20MW NEP setup fed by a 150MWth LEU reactor to drive its pumpjet propulsor. Notably, the setup on the Suffren-class is only designed to use the nuclear-electric solution up to a certain speed (let’s say 20-25 knots) for relatively silent transit. Beyond 25 knots the submarine has to rely on its backup conventional gearing – which is understandably more noisy – in order to attain higher speeds (up to a maximum of 30+ knots I would presume).
The Expression of Interest (EoI) documentation above also calls for the Indian NEP setup to drive the submarine to a maximum forward speed of 25 knots. It’s likely that the P77 would also have to fall back on a conventional gearbox setup when required to go faster (again, let’s say it can do a maximum of 30 knots or more). So P77 might be carrying both types of transmission systems, switching back & forth as necessary, just like on the Suffren.
Either way, even without the NEP this reactor should put the P77 in a very good place in terms of speed, stealth and performance when going up against any given opponent SSN, such as the new Type-093B of the Chinese PLA Navy. In fact, the P77 is very likely to enjoy an outright advantage in those regards against the Chinese boats, but especially in terms of stealth, considering the OK-650B’s natural-circulation design (no need to run noisy pumps to cool the reactor) is likely to be carried over – barring any considerable improvement the PLAN manages to make in the decade-plus it would take for the P77 to arrive.
NEP/TED has so far remained a technology mostly found on Western nuclear submarines, such as France’s Triomphant & Suffren classes, the United States’ experimental USS Glenard P. Lipscomb and upcoming Columbia-class SSBN (which likely has the same TED as the UK’s upcoming Dreadnought-class). If implemented, the NEP/TED on the Indian submarines would mark a significant ‘coming of age’ for the country’s growing shipbuilding & heavy electricals industry.
Also worthy of note is the fact that, at least according to the the EoI document above, the nuclear-electric setup being pursued by the Indian Navy clearly calls for the NEP to drive a Pump-Jet Propulsor. Is that enough reason to assume the P77 will have a pumpjet instead of a traditional screw? Remains to be seen, but it would be surprising if it doesn’t.
This same reactor and NEP setup are also likely to drive India’s upcoming S5-class of next-generation SSBNs. The S5s will be much larger than the 6,000-7,000 tons (surfaced) Arihant & Arihant Stretch. The S5 is believed to displace between 13,000 to 14,000 tons surfaced, with at least 12 vertical launch silos. However, the S5s will perform a very different mission (deterrence), hence their reactors will have to be modified to cater to the needs of the SSBNs’ unique power delivery pattern (smooth and gradual acceleration) compared to the rapid stop-starts that might be required in SSN operations…though future submarine doctrine might evolve to encompass both capabilities as per need.
Sensors
Based on reports from official DRDO publications (pictured below) it’s evident that R&D work on both Conformal Bow-Array sonars as well as Planar-Arrays (ostensibly used for flank-array & towed-array setups) is/has been ongoing in India for several years. While it’s difficult to say which R&D program might or might not find a real-world application on upcoming submarines, I think it can be safely said that there’s at least a determination in the Indian Navy to advance past the older Cylindrical-Array sonar setup used in the bow of the current generation of Indian nuclear-powered boats.
Among SSNs that are currently being built, the British Astute-class comes to mind as one that has a conformal bow array.
Over the last few years, the Instrument Research & Development Establishment (IRDE), the DRDO’s premier electro-optic lab, has successfully transferred its technology of optronic periscopes – which do not penetrate the boat’s pressure hull – to the private sector for commercialization across various submarine classes. A more capable and less power-constrained version is all but certain to find use on the SSN project.
With the B2 reactor’s vast bank of power output on tap, all of the sensors on the P77 will likely be able to operate to their full potential, which means the SSN’s sensors can operate continuously for longer periods of time and register contacts (actively or passively) at significantly farther ranges compared to a similar sensor with similar technology but operating within the electrical power input limitations of conventional diesel submarines.
Weapons
While there’s yet no official word on this (and it seems the final design of the submarine itself may or may not yet be frozen), I would estimate that using a 190MWth/60MWe reactor, there would be enough power on tap for the P77 SSN to incorporate additional mission sets beyond pure hunter-killer duties. Speculation among reliable sources indicate that this could include carrying a pack of vertically-launched subsonic Land-Attack Cruise Missiles (LACMs) like the Nirbhay/LRLACM with a range exceeding 1,000 kilometers. A submarine-launched version of the Ramjet-powered supersonic BrahMos-NG currently in development is likely for anti-shipping roles out to a shorter range of around 300 kilometers. The recently tested LRAShM hypersonic boost-glide vehicle (sans the large solid booster) might also comprise a potential loadout for carrying out Anti-Ship/Carrier-killing duties.
But the primary armament of the P77, or for any other SSN, would be its 533mm Heavy-Weight Torpedoes (HWTs). While the P77 would likely be compatible with a wide range of 21-inch HWTs that the Indian Navy uses, its primary load-out will likely consist of a next-generation system known as EHWT, which would itself probably have a small Pump-Jet Propulsor (PJP) – a product of long-term research by Indian labs into the technology, which might have likely fed lessons & informed the development of a larger one for submarines.
Configuration
It remains to be seen what the final configuration of the P77-class SSN will be like, but at this point I would estimate its surfaced displacement to be somewhere between 5,000 and 7,000 tons. P77s will likely be larger than the 5,300 ton French Barracuda/Suffren-class but possibly smaller than the Royal Navy’s 7,400 ton Astute-class and the US Navy’s 7,900 ton Virginia-class (Blocks I-IV specifically, Block-V is significantly larger).
I personally do not believe in the reports in some sections of media (like this article from the Times of India) that say that the P77 will displace 10,000 tons. Such a displacement would make the P77 similar to the Improved Akula-class in terms of displacement (and size). That would be entirely unnecessary for the Indian Navy’s purposes. Either way, I think we’d do well to believe that the P77 would incorporate an entirely new hull design compared to the Arihant – as I believe that the Arihant-class’s internal bulkheads would probably be too small to accommodate the new 190MW reactor compartment.
Assuming that the SSN program underwent as much design evolution as the S5 SSBN did (the change in project designation from P75A to P77 might itself indicate a significant change in configuration), it’s likely that the possible inclusion of NEP might also affect the length & displacement of the final design – a submarine with NEP would displace more & be longer than one with just conventional gearing.
Timeline & Conclusion
All said and done, I think we can expect the first P77 boat to be commissioned in the mid- to late-2030s. This is assuming the construction starts within the next two years, with a build time of between 8 and 10 years followed by at least a few years of sea trials. Much would also depend on how much technology being rapidly iterated over the Arihant-class finds application on the P77.
It’s worth noting that even going by what’s known so far, every single Arihant-class boat appears to be significantly different from the last owing to continuous technology insertion i.e. improved reactor in boat S3 and hull extension in boat S4. It’s also possible that the upcoming ‘S4*’ (fourth & presumably last boat of the class) might turn out to be having a pumpjet. This is if a decision were taken to de-risk the P77’s and S5’s next-gen propulsion setup by testing the pumpjet on the S4* instead of putting both of the untested technologies (NEP & Pumpjet) on the SSN & S5 SSBN directly.
A staggered technology-insertion program is also likely. This could be why the requirement was broken down into 2+4 boats instead of all 6 at the same time. This might get further broken down into 2+2+2 in the future.
It’s also possible that the eventual requirement of hulls will be extended beyond the six P77s currently sought, to twelve – given that six might be too few to fulfill the wide frontage of offensive & defensive needs of the Indian Navy which include providing protection & escort to SSBNs as well as Carrier Battle Groups.
Keeping in mind the construction of a new large, higher capacity, dry-dock at SBC Vizag (image below), it’s very likely that at some point within the end of this decade (2020s), the Indian Navy could have both the new SSNs and S5-class SSBNs under construction at the same time. They might also be delivered simultaneously over a period of time in the next decade (2030s). The new dry dock appears to be wide enough to accommodate up to three hulls side-by-side, each in various stages of construction/fitting out – much the same as the BAE facility at Barrow-in-Furness that builds the Astute-class.
The primary subcontractor for the build program is likely to be the Indian engineering major Larsen & Toubro (L&T), the same company that built entire hull sections for the Arihant-class (and interestingly, the pressure vessel that encapsulates the massive fusion reactor at ITER. No kidding on the ‘engineering major’ part). L&T has facilities at Hazira on the country’s west coast where hull sections can be pre-fabricated and transported via barge to SBC Vizag on the east coast for final assembly.
The two dry-docks in Vizag – one of which looks like it’s shaping up to accommodate up to three hulls side by side, while the other (existing) one is known to be able to house two hulls, one behind the other – can together carry out simultaneous build/outfitting of up to FIVE nuclear submarine hulls at any given time. A very extensive capacity only present with a handful of countries.
Which class of upcoming boats (S5 & P77) will be assembled at which dry-dock remains to be seen. Personally, I would argue that it would be prudent to have the SSBNs be built at the existing dock as they are fewer in required number (only four S5s are expected to be built) compared to the SSNs (six confirmed required, with high likelihood of follow-on orders) which may be able to take better advantage of the larger facility.
As far as the S5 is concerned, being a strategic platform (for carrying nuclear weapons) the funding modalities for these boats will be largely secret. Probably in part owing to India’s status as a non-signatory to the nuclear Non-Proliferation Treaty. None of the public reporting such as cabinet approvals or funding details applied to the P77 will likely apply to the S5, so its progress will not be as easy to track using publicly-available sources.
But I personally think it’s safe to assume that the S5 is further along in its program than the P77.
Thank you for reading!
