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. 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, 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. 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, 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 weapons – 1.7kt boosted fission W25 warheads – launched from ships to very high altitudes over the southern Atlantic Ocean. Such an explosion releases a burst of X-rays 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 Argus returned key data about a related effect, the