Whenever I think about defence of A&N islands, I always think about the Battle of Iwo Jima. My reference was mostly what I've seen about it on the twin movies: Flags of our Fathers and Letters from Iwo Jima as well as episodes of The Pacific that focused on this battle. But this declassified video presents an entirely new perspective to those stories as it details the pre-landing phase of the battle:-
Iwo Jima was obviously a hard fought victory for a much superior American force and it became so because of the entire Japanese Army Division and its numerous artillery pieces that were defending Iwo Jima even after the Japanese Navy lost control of the seas around the island.
In comparison, our situation seems to be where we have only the 91st Infantry Brigade to defend the entire A&C islands and Lakshadweep as well. And the 91st isn't even stationed on these islands, they are in Kochi.
Now we are talking about making Great Nicobar into a major economic center and transshipment hub. Just for comparison, Great Nicobar alone is 4385.7% larger than Iwo Jima. In wartime, we might not even be able to spare an entire brigade to defend it.
Which means that our entire strategy is to not lose the Naval Fleet Battle for control of Andaman sea in the first place. Meanwhile, everyone is aware of the Chinese fleet size growth and also their Marine capabilities growing especially with Type 075 LHA and Type 071 LPD ships that indicate that PLAN is looking to create a marine capability comparable to USA.
I myself have been against creating an Indian Marine Force, and also have been against reducing the number of active combat units on our borders with China and Pakistan. And we all know that the size of our military is already too large in proportion to our budget so we can't raise new units anymore.
And yet A&C will be practically defenceless if we lose the Naval Battle against PLAN (which seems likely if our Naval buildup doesn't gather pace). And yet the third carriers, etc are not coming anytime soon. My only hope at this point is that America is able to put enough pressure on PLAN so that in wartime, they become unable to send most of their fleet to take on Indian Navy. But even relying on that hope is inadvisable because for USA, it will be a win-win if China and India weaken each other and India loses these islands permanently. For them, both India and China are rivals.
TL;DR setting aside the possibility of whether PLAN will be to send enough forces to IOR to be able to mount a large amphibious attack on A&C islands, what is our defence plan if this actually happens.