Editing Anti-ballistic missile (section)

===1940s and 1950s===
[[File:Wizard missile concept.jpg|thumb|right|1946 [[Project Wizard]] missile]]
[[File:NIKE Zeus.jpg|thumb|right|Launch of a [[US Army]] [[Nike Zeus]] missile, the first ABM system to enter widespread testing.]]

The idea of destroying rockets before they can hit their target dates from the first use of modern missiles in warfare, the German [[V-1 (flying bomb)|V-1]] and [[V-2 rocket|V-2]] program of [[World War II]].

British fighters destroyed some V-1 "buzz bombs" in flight, although concentrated barrages of heavy anti-aircraft artillery had greater success. Under the lend-lease program, 200 US [[90 mm Gun M1/M2/M3|90 mm AA]] guns with [[SCR-584 radar]]s and [[Western Electric]]/[[Bell Labs]] computers were sent to the UK. These demonstrated a 95% success rate against V-1s that flew into their range.<ref name=cav>Gregory Canavan, [http://missilethreat.wpengine.netdna-cdn.com/wp-content/uploads/2012/11/20030000-Heritage-canavan.pdf "Missile Defense for the 21st Century"] {{webarchive|url=https://web.archive.org/web/20150713192027/http://missilethreat.wpengine.netdna-cdn.com/wp-content/uploads/2012/11/20030000-Heritage-canavan.pdf |date=13 July 2015 }}, Heritage Foundation, 2003, p.3</ref>

The V-2, the first true ballistic missile, has no known record of being destroyed in the air. SCR-584's could be used to plot the trajectories of the missiles and provide some warning, but were more useful in backtracking their ballistic trajectory and determining the rough launch locations. The Allies launched [[Operation Crossbow]] to find and destroy V-2s before launch, but these operations were largely ineffective. In one instance a Spitfire happened upon a V-2 rising through the trees, and fired on it with no effect.<ref name=cav/> This led to allied efforts to capture launching sites in Belgium and the Netherlands.

A wartime study by Bell Labs into the task of shooting down ballistic missiles in flight concluded it was not possible. In order to intercept a missile, one needs to be able to steer the attack onto the missile before it hits. A V-2's speed would require guns of effectively instantaneous reaction time,{{dubious|date=September 2019}} or some sort of weapon with ranges on the order of dozens of miles, neither of which appeared possible. This was, however, just before the emergence of high-speed computing systems. By the mid-1950s, things had changed considerably, and many forces worldwide were considering ABM systems.<ref name="Ramsey">{{Cite book|url=https://books.google.com/books?id=aUk5DAAAQBAJ&q=By+the+mid-1950s,+things+had+changed+considerably,+and+many+forces+worldwide+were+considering+ABM+systems.&pg=PT28|title=Tools of War: History of Weapons in Modern Times|last=Ramsey|first=Syed|date=2016-05-12|publisher=Vij Books India Pvt Ltd|isbn=9789386019837|language=en}}</ref>

The American armed forces began experimenting with anti-missile missiles soon after World War II, as the extent of German research into rocketry became clear. [[Project Wizard]] began in 1946, with the aim of creating a missile capable of intercepting the V-2.

But defences against Soviet long-range bombers took priority until 1957, when the Soviet Union demonstrated its advances in ICBM technology with the launch of [[Sputnik program|Sputnik]], the Earth's first artificial satellite. The [[US Army]] accelerated development of their [[LIM-49 Nike Zeus]] system in response. Zeus was criticized throughout its development program, especially from those within the [[US Air Force]] and nuclear weapons establishments who suggested it would be much simpler to build more nuclear warheads and guarantee [[mutually assured destruction]]. Zeus was eventually cancelled in 1963.

In 1958, the U.S. sought to explore whether airbursting nuclear weapons might be used to ward off ICBMs. It conducted several test explosions of low-yield [[nuclear weapon]]s – 1.7kt boosted fission [[W25 (nuclear warhead)|W25 warheads]] – launched from ships to very high altitudes over the southern Atlantic Ocean.<ref>Nuclear Weapon Archive.org. [http://nuclearweaponarchive.org/Usa/Tests/Argus.html Argus] {{Webarchive|url=https://web.archive.org/web/20060911023819/http://nuclearweaponarchive.org/Usa/Tests/Argus.html |date=11 September 2006 }}.</ref> Such an explosion releases a burst of [[X-ray]]s in the Earth's atmosphere, causing secondary showers of charged particles over an area hundreds of miles across. These can become trapped in the Earth' magnetic field, creating an artificial radiation belt. It was believed that this might be strong enough to damage warheads traveling through the layer. This proved not to be the case, but [[Operation Argus|Argus]] returned key data about a related effect, the [[nuclear electromagnetic pulse]] (NEMP).