"Jive" (an ex-USN electronic warfare (sonar) specialist submariner through to the 2000s) here https://youtu.be/stoYRQKhKtQ and below
provides a briefing on India's nuclear submarine Arihant class/"Advanced Technology Vessel" project. From the video:
1:40 - Project 932 (for a submarine reactors and nuclear subs (SSBN and SSNs) began in the 1970s.
2:10 - in the early 1980s the top Russian military leadership announce and commence Transfer of Technology (ToT) of nuclear subs especially reactors to India.
3:00 as a technology and training demonstrator, Soviet Charlie-class SSGN, is leased to India for 4 years from 1987 being called INS Chakra I.
4:15 another demonstrator, a Russian Akula class SSN, is leased to India for 10 years from 2012, called INS Chakra II. At end of lease in 2022 it is expected India will buy it outright.
5:20 Jive is wrong in saying the keel of INS Arihant was laid down in "2009". 2009 was the year Arihant was launched - see here "July 26, 2009" and here. Meanwhile INS Arighat's keel was laid down 2011. Both "very short" for SSBNs, so have few meters/little space for missile compartments.
7:00 Bow of Arihant very similar to Kilo class, according to photos Jive presents. Jive then assumes Arihant has the bow of the design and size/beam of a diesel electric Kilo sub. Jive assumes Arihant therefore has 6 x 530mm torpedo tubes (capable of launching "Kalibr" [or Klub?] land attack SLCMs.
8:12 Jives assumes the Arihant has an USHUS-2 indigenous bow sonar system, based in Russian Rubicon-M
8:42 The sail and non (hull) penetrating masts (eg. photonic) etc. Non penetrating reduces flooding risks.
10:40 Arihant's ballistic missile capacity is minor, but a good start.
11:45 Combat system (Russian derived?) and steering/diving
13:50 Exterior. "INS Arihant at sea."
Jive concludes India developing several SSBNs and SLBM types is a "huge advance" done quickly and in line with non-proliferation treaties [except for proliferating the nuclear weapons? Noting some international reactions to 1998 nuclear tests.].
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Submarine Matters has numerous articles on Arihant, Arighat, submarine reactors, SLBMs and India's whole submarine fleet since 2009.