It’s been a while since I was last briefed some on some of the programmes you mentioned, SM-3, but I’m sufficiently familiar with all of them to take a stab at answering your question.

There are in fact three programmes – THAAD, Patriot PAC-3, and Standard Missile 3 (SM-3) – that we need to consider. The way that these evolved was partly constrained by the existing hardware that both services already possessed.

Mr. Mercurius, thanks for your informative reply. I think to know the history of weapons development is important, so as to understand their use and how & what future weapons will be developed.

Actually, I referred to Patriot and Thaad as a single system because both are complementary to each other in targeting in the exo and endo atmospheres respectively, exactly like India’s AAD-PAD combination. It is now clear that Patriot and Aegis have actually evolved independently from pre-existing rudimentary systems, whereas I thought they were begun separately to address the latest ballistic threats.