Might Japan one day sell India a for export specification submarine similar to Japan's Yushio-class design - with pressure hull steel equivalent to High Yield HY120 and air independent propulsion (AIP)? (Photo via Wikipedia).
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Japanese Prime Minister Abe's Indian visit in mid September 2017 raised the issue of a possible future sale of Japanese submarines to India. The sale would be under Project-75(I) to supply the Indian Navy with 6 AIP submarines. The re-issued and extended RFI might be steadily giving Japan a better chance of winning. Japanese Soryu submarines have been mentioned, but they may be too highly classified and expensive. Hence a for export specification Japanese design might be more likely.
Ever since Pakistan introduced MESMA AIP into its latest 3 Agosta submarines India has been intent on also acquiring AIP for its own submarines. China also has (Stirling) AIP (locally developed or bought from Sweden) in its Yuan submarines.
India's Defence Research and Development Organisation (DRDO) has long been developing a fuel cell AIP technology, but this is a very difficult - so much so that Germany is the only demonstrably successful fuel cell AIP developer.
Recent border friction with China and increased Chinese submarine activity in the Indian Ocean has underlined to India that it needs more powerful conventional submarines quickly. India's perpetually delayed Project 75(I) AIP submarine selection project is therefore being accelerated.
Chances that Japan is now a serious contender in Project 75(I) may be increasing. Japan builds highly capable large submarines (which can carry more missiles, torpedoes and mines) and has long experience with Stirling AIP (probably bought from Sweden). Japanese sale of Stirling AIP to India would likely require involvement of Sweden. Stirling AIP is likely superior in quietness and low heat signature to MESMA AIP. A submarine purchase from Japan would also boost a key regional strategic friendship against India's and Japan's strategic competitor, China.
Regional friendship is something Project-75(I) competitors (Germany, France, Sweden) in distant Western Europe, cannot deliver. Northeast Asian nations, (Siberian) Russia and South Korea, also competing for Project-75(I) are both careful not to antagonise China.
Japan's large 2,900 ton (surfaced) Soryu submarines might be uncompetitive as they may be priced at US$1.5 billion each. This is in comparison to US$1 billion for 1,800 ton 75(I) competitors.
Japan does not want its most tightly held submarine secrets finding their way to China - so Soryu technology may be too sensitive. Japan would be wary of India's exchange of submarine high technology with Russia in the form of Kilos, naval reactors and SSNs. Russia also shares submarine technology with China.
Price and secrecy may mean that Japan might prudently supply lower specification for export submarine technology to India - particularly concerning Japan's Top Secret high yield pressure hull steel. Lower specification steel might perhaps be equivalent to the pressure hull steel in Japan's Yushio-class design ie. Japanese NS80 grade (equivalent to still advanced US High Yield HY120 steel - see the Table on Submarine Matters).
When eventually decided India's Project-75(I) competition will be a major win for any of the competitors.
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