P75I is necessary to develop the industry before P76 enters the fray. The same as MRFA to AMCA transition. We obviously wanna get the P76 design bit done, like we did with AMCA, so we know what OEM-related tech to focus on for their assistance before construction begins, like the diesel engine.
As for examples of other navies. The big ones with India-class requirements develop different blocks with new AIP tech, but are largely indigenous. For example, Korea (3 classes, 2 with different AIPs) and Japan (2 classes, 1 with AIP, one without). The small ones only operate 1 class at a time, even Australia. Australia did not want AIP or Li-ion battery, they wanted their traditional snorkel method that put them above water only for a few minutes. The Collins class sucked in all the oxygen it needed, stored it and ducked under water again. They didn't want the risk of dealing with new tech. The Russians and Japanese plan to skip future AIPs in favor of battery-only designs.
So we are following in SoKo's footsteps, 2 classes with 2 AIP designs, one indigenous, one foreign, eventually transitioning to Japan/Russia style with fully indigenous designs built in large numbers in multiple blocks with new tech in each block, no different from our P-15 and P-17 programs. The Korean KSS-III is composed of 9 subs in 3 blocks.
DRDO is designing a new AIP for P76, although the base design is the PAFC.
Both PAFC and the Spanish BEST are the most modern future-ready designs when it comes to AIP 'cause both do not use stored hydrogen, it's produced on demand. The German PEM requires stored hydrogen, which is hazardous and takes up too much space.
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