The IN is looking for an ocean going SSK, along the lines of the now-cancelled Shortfin Barracuda (Attack Class) SSN of the Royal Australian Navy. A larger boat is required than the Scorpene, which can carry more fuel combined with a proven AIP module. As per the Navy, the Scorpene will not be sufficient for this task. They were also looking to incorporate a VLS module into Project 75I. I am not sure what happened with that requirement.
The Type 216 from Germany and the DSME-3000 (export variant of the KSS-III) from South Korea were the pair of candidates that could meet those Navy requirements. Threat perceptions and capability requirements have changed from when the Project 75 contract (Scorpene program) was signed and the Navy is looking for a vessel to meet those threats. They cannot afford an all SSN fleet, due to the high cost and long lead time of Project 75 Alpha.
The Project 75I program was supposed to be a stop gap SSN, till the Project 75A starts rolling out. Obviously that is not happening right now, as the P-75I is listing aimlessly. Many are to blame for this mess, but the primary actor is the Indian Navy;
^ The navy - in her usual obstinance* - refused to budge from the Project 75I program. They did not want to even entertain the idea of getting additional Scorpenes and wanted only the Project 75I. This delay wasted precious time and the submarine arm continued to dwindle further. See the date of the very first post in this thread (25 Oct 2014). This tamasha has been on for much earlier. Naval Group had reportedly offered to continue to the Scorpene line in India and build three additional boats, but the Navy insisted on the P75I.
^ The navy wanted an unobtanium boat with even more unobtanium manufacturing requirements. The OEMs balked at them and one after the other, they kept dropping out. MoD insisted on local production with liability resting on the OEM. Which OEM will sign up for this nonsense? Finally after relaxing the requirements, TKMS and Navantia re-entered the fray. Hanhwa has reportedly dropped out, perhaps due to the fact that there is no Indian partner left. TKMS has partnered with MDL and Navantia has partnered with L&T.
^ After the numbers dropped dangerously low, the Navy finally decided to order three additional Scorpene boats. What happened to the Navy - that all of a sudden - three additional Scorpene boats now suddenly look promising? But no Admiral (or politician or babu) will ever shoulder the blame for this delay. Had the Navy taken up Naval Group's offer, the first of three Scorpenes could very well have been on her way in construction. Now the Navy will have to wait till the early 2030s for the first Scorpene of the second batch to arrive.
^ The very idea of incremental capability upgrades is lost on the Indian Navy. Project 75I and IAC-2 are two excellent examples of this. Now the Navy has had to eat humble pie on both programs. They were making plans that the civilian bureaucracy had no intention of ever funding. The Navy was aghast when BARC wanted the Navy to fund the development of a nuclear reactor for IAC-2. The Navy thought that BARC would just gleefully jump on to the program and provide a nuclear reactor to the Navy with a red bowtie around it.
^ The ones whose lives are on the line - due to this malaise - are YOs (Young Officers), JCOs and NCOs. One YO even remarked (when referring to the submarine fleet, right after the Sindhurakshak incident), "Sir, we are sitting on ticking time bombs." When lives are lost, gift a Vir Chakra to their next of kin, sing Jana Gana Mana or Vande Mataram and then move on. Project 75I is a desirable program - in principle. But that does not mean you throw everything out the window and hold your breath, till you get what you want.
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* Usual Obstinance: This was all during the time of an euphoria/renaissance session that Naval HQ was experiencing in the middle of the previous decade. There were grandiose plans of EMALS-equipped aircraft carriers, a sizeable fleet of phoren MRCBF, nuclear powered submarines, etc. For Navy Admirals - exercising with US Navy Carrier Battle Groups during Malabar exercises - was love at first sight. A Nimitz Class aircraft carrier with AEW aircraft, naval fighters, ASW helis, etc combined with her battle group of AEGIS-equipped surface combatants and Virginia Class nuclear powered submarines were an aphrodisiac so powerful....that our Admirals had to have the same.
Navy Admirals were publicly announcing these programs (media events, press conferences, Navy Day, etc) and proudly claiming that there were no budgetary shortfalls envisaged. We all know how that panned out. That fever got a strong hold even on BRF, as this was the gyan --->
"Without a CATOBAR aircraft carrier, the Indian Navy will lose everything. CATOBAR is a must have."
Led by the Risk Assessor-in-Chief, who boldly proclaimed that 57 F-18SHs were going to be purchased by the Indian Navy, along with a 65,000 ton EMALS equipped aircraft carrier and would influence events all the way from Alaska to the South China Sea. And just like at Naval HQ, when asked where the funds for these fantasies were going to come from, the standard answer on BRF was, "Well, money should be there!"
CATOBAR aircraft carrier was just an excuse to get the F-18SH into the Indian Navy. Obviously the American apologists on BRF could never say that openly, so CATOBAR was the crutch to fall on. Even Ashley Tellis peddled that theory that the Indian Navy requires minimum of 65,000 tons to be a viable aircraft carrier. Wonder what the 42,000 ton Charles De Gaulle is then? She is a CATOBAR vessel and nuclear powered. She is limited only by the food carried onboard, just like any other CATOBAR aircraft carrier.
Now that the F-18SH lost the contest, the CATOBAR boys are all silent
Now no more gyan about CATOBAR aircraft carriers 
