You will never devlop the skill and protocols you need for a product unless you have been responsible for the entire PLM of the product, in ToT your role starts after the original manufacturer has gone through design validation, design Fmea, process fmea, early launch containment, DVP&R, non conforming material process. So by the time the product reaches you, the design, the process, the validation, and quality check for every product is frozen. In other words, you don't get to learn anything in the process. You dont develop engineers and managers who can innovate and lead from thier own experience, you get engineers and managers who can follow instructions.
Take the Brahmos co-development for example, without Russian tot especially on the propulsion and seeker, we wouldn't have such a weapon in our inventory today. We have it, because we used the co-development to include what we was able to do so far and got the part that we couldn't do from the Russians. Now we are at a level to further develop the missile to new varients, applications and even with NG versions in mind.
Same goes for the Maitri SAM, which also is developed according to Indian requirements with the techs that we can't provide and is meant to add French parts and capabilities that we don't have yet.
FGFA, we include materials, coatings, avionics, while we get ToT of the most powerful AESA radar, NG engines and other techs that we aren't able to develop on our own...
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On the other side we have LCA, that sadly was developed with waaay too many indigenous parts in fields where we wasn't realistically able to provide something and that's why the project suffered all the delays and problems and why it will be inducted only decades behind schedule.
Also the Kaveri engine, developed alone, failed completetly and not ready to power an operational fighter anytime soon if we keep doing it alone. So all the money and time was wasted and now we search for a co-development or JV to fix the problems.
LCA and Kaveri as programs were still important, but overestimating your capabilities with the wrong idea that you have to develop anything on your own will lead us nowhere as these developments sadly proved. As I said, times have changed and today we can demand way more than we could in the past and why co-developments and JVs under our requirements are so important for India, if we don't want to remain a generation behind China, Russia or the West and want to catch up faster.