Air-launched ballistic missile

An air-launched ballistic missile (ALBM) is a ballistic missile launched from an aircraft. An ALBM allows the launch aircraft to stand off at long distances from its target, keeping it well outside the range of defensive weapons like anti-aircraft missiles and interceptor aircraft. Historically, once launched the missile was essentially immune to interception due to a lack of capable anti-ballistic missiles, with those few that did exist being limited to known static positions. This combination of features allowed a strategic bomber to present a credible deterrent second-strike option in an era when improving anti-aircraft defences appeared to be rendering conventional bombers obsolete. However, by the 1990s surface-to-air missile technology had innovated to the point of allowing the interception of such weapons (especially in their terminal phase) from road mobile systems, albeit at a lower PoK. By the early 21st century capable, dedicated, ABM systems from several nations had been deployed in significant numbers (with examples including upgraded MIM-104 Patriot and S-300, THAAD, SM-3, and S-400), spurring further innovation in hypersonic glide vehicles to penetrate such systems and keep ballistic missiles capable.

The ALBM concept was studied in the US as a way to ensure the usefulness and survivability of their large bomber fleet. After testing several experimental designs as part of the WS-199 efforts, the U.S. Air Force began development of the GAM-87 Skybolt missile with range on the order of 1,150 miles (1,850 km). The only other major force relying on strategic bombers was the Royal Air Force, who also selected the Skybolt to arm their V bomber fleet. The Soviet Union moved their strategic force directly to Intercontinental Ballistic Missiles.

Skybolt ultimately failed several key tests, while the US Navy's UGM-27 Polaris offered the same advantages and more. Skybolt was cancelled, leading to the Skybolt crisis and an agreement to sell Polaris to the Royal Navy as part of the Nassau Agreement. The concept saw little active development until the 1970s when ICBM warheads began to become accurate enough to attack other ICBMs while they were still on the ground. The US carried out several experiments using existing missile designs dropped from cargo aircraft, but ultimately abandoned this line of research entirely. No further strategic ALBM development has been carried out by the US, and this class of missile never saw active use.