|Fig. 1: Source: Wikimedia Commons. - An LGM-30 Minuteman III missile (ICBM) soars in the air after a test launch.|
The Cold War marked a unique change in how global warfare was carried out. Nuclear warheads was the game changer that made super powers like the United States and Russia think twice about plunging into all out war because of the shear destructive power of nuclear bombs including ICBMs (intercontinental ballistic missiles). Since the invention of the ICBM, countries with nuclear warheads have offensive capabilities far greater than their defensive capabilities. In an attempt to improve defense capabilities against nuclear attack, various national missile defense programs were developed. This article will briefly discuss the United States programs and measures to guard against incoming nuclear missiles.
Initially nuclear bombs dropped from aircraft were the most likely major threat. To answer this, the army initiated Project Nike, designed to develop missiles that would intercept incoming enemy aircraft. The system was eventually extrapolated to be used on incoming nuclear missiles. The latest model, the Nike-Zeus could reach speeds up to 8,000 mph but suffered from several technical flaws, that were believed to be uneconomical to overcome.  Because Nike-Zeus missiles were ground based, the intercept point with ICMBs was almost guaranteed to be close to or over American soil albeit at extremely high altitudes.
Thus the goal changed to space or satellite based missile defense systems. This new phase was called Project Defender. This began in 1958 as a top-secret high profile venture that employed many of the nation's best scientists. One idea called Bambi, Ballistic Missile Boost Intercepts was to destroy Soviet ICBMs in the boost phase where the missiles were rising into space. The project was eventually envisioned to have space-based battle stations that launched rockets with 60-food rotating wire nets containing destructive steel pellets. Such an idea was actually tested on the Atlas and Titan missiles.  Although these tests were successful, there was no solution to attacks on the orbiting battle stations and was eventually canceled in 1968.
Another major goal was to protect the continental United States by the Sentinel Program in 1963. This system employed long range Spartan missiles and shorter range Sprint missiles. However, several problems with the system include: 
Interception of multiple nuclear targets was increasingly more difficult
Deploying the system would likely invite another expensive arms race for defensive systems
The coverage area was limited because of the short range of the Sprint missiles
The Safeguard Program was a scaled down version of the Sentinel Program, that focus on specific areas of the United States. Most notably, major cities and missile silos where given the higher priority.
Eventually such issues guided both the United States and the USSR to sign the Anti-Ballistic Missile Treaty. This treaty allowed each country to select on key area to defend against ICBMs. However in 2002, the United States withdrew from the ABM Treaty. Russia answered by withdrawing from the START II Treaty (Strategic Arms Reduction Treaty) which bans ICBMs having multiple warheads. The most recent plans the United States has made is to place anti-nuclear systems on navel vessels. 
Creating a defense network has not only been a technological challenge, more importantly it has been a political challenge. It seems as though every step taken toward defense systems strains international relations.
© Paul Theodosis. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 New Missile Defences in Europe: Shooting Down a Plan, The Economist, 24 Sep 09.