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 probability of kill(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.