The United States was also diligently working on ABM systems starting from the early 'Sixties (see Nike Zeus and Nike-X), and culminating in the Safeguard system, activating in 1975 as the Stanley R. Mickelson Complex, which protected the Minuteman silos of the 321 SMW out of Grand Forks AFB. The Safeguard System–a scaled down version of Sentinel, which itself was a vastly scaled down version of a broad reaching ABM system which former Secretary of Defense Robert S. McNamara rejected on the basis of cost and ultimate ineffectiveness against the growing Soviet ICBM arsenal–was implemented at only this one site in accordance with SALT I and ABM treaties. Safeguard was comprised of two layers–the LIM-49 ‘Spartan’ and the LIM-99A ‘Sprint’. The Spartan was a late mid-course/early terminal-course interceptor with an enhanced radiation (i.e. high neutron) warhead of ~5MT, while the Sprint was a mid- to late-terminal phase interceptor with a nominal 1KT ER warhead. In testing, Sprint actually demonstrated hit-to-kill (i.e. physical interception) capability, albeit only against single targets; the radar and control systems of the time were extremely limited in tracking multiple intercepts and could have been overwhelmed by simultaneous bogeys, which in part explains why the system was operated for only a few months before being decommissioned due to the extreme cost and questionable lack of security it provided, as the launch response time of the Minuteman II and oncoming Minuteman III missiles was such, and DEW line detection was effective enough that even an attempt at a disarming first strike would likely allow enough time to launch said missiles before they could be disabled.
The Soviets implemented the S-35 (later upgraded to S-135) system, which in configuration and capability roughly equivalent to Sentinel, around Moscow. Again, the effectiveness of this system in a real shooting match against multiple targets is highly questionable. This is the extent of practical implementation of Soviet and later Russian ABM systems, though like the United States they have conducted advanced research into space-based weapons and directed energy (laser and particle beam) systems, with about the same level of effect (i.e. not past rudimentary and low-power proof-of-concept demonstrators). There was no particular “catching up” that the United States needed to do in terms of ICBM-ABM; although the Soviets spent a lot more time developing weapon systems, actual capabilities were generally pretty comparable, though the Soviets concentrated on larger throw weights and greater mobility for ICBM basing giving them a perceived (but not practical) advantage.
“Antiaircraft” missiles are basically useless against ballistic missiles; the former are intended to hit targets moving at <1500 mph, while the later have to intercept targets moving at an order of magnitude higher speed.
Reagan’s Strategic Defense Initiative (or as deriders called it, “Star Wars”) was really little more than a loose visionary concept of impenetrable missile defense. Reagan himself basically had no clue about the technical implementation, and most advocates had either hopelessly optimistic estimates about the progression of missile defense technology and the effectiveness of such a system vis a vis increasing penetration-capable MIRV-ICBM proliferation, or acknowledged that the effect of such a system was limited to the deterrent effect of providing only point defense of strategic sites (such as missile complexes) to prevent disabling strikes and would not be the protective umbrella that Reagan envisioned.
The current state of the art of ICBM defense for the United States is a very limited and only lightly tested Ground-Based Mid-Course Defense system (~20 missiles in silos in Alaska and California), plus proposals to emplace GMD systems in Japan and Eastern Europe, plus USN Standard Missile 2 and 3 systems which have demonstrated a limited but successful intercept capability, including the recent shoot-down of a re-entering satellite. The Russian capability is more limited with the S-135 system, although they have more extensive theater-level ABM systems which might, at their extreme, provide some measure of defense against ICBMs. Neither nation, nor any other, can claim anything like an effective system against a concerted attack, nor will such systems defend against nap-of-the-earth supersonic cruise missiles, pop-up short-range torpedo missiles, or nuclear weapons shipped in by slow boat and subterfuge. So the practical effectiveness of even a reliable ICBM-ABM system is questionable at best.
Stranger