On October 24, 1974, a Minuteman ballistic missile was dropped from a Lockheed C-5A Galaxy transport and fired in mid-air to test the feasibility of protecting ICBMs from a Soviet first strike by deploying them in aircraft.
An air-launched ballistic missile or ALBM is a ballistic missile launched from a bomber. 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. Once launched, the missile is essentially immune to interception. This combination of features allowed a strategic bomber to present a credible deterrent second-strike option in an era when improving anti-aircraft defenses appeared to be rendering conventional bombers obsolete.
The ALBM concept was only seriously studied in the US, largely 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 USAF began development of the GAM-87 Skybolt missile with range on the order of 1,150 miles...
Skybolt was canceled...
In the early 1970s, the USAF tested air-launching a Minuteman ICBM from a C-5A Galaxy transport aircraft. On 24 October 1974, Space and Missile Systems Organization successfully conducted an Air Mobile Feasibility Test where a C-5A Galaxy aircraft air-dropped the 86,000-pound missile from 20,000 feet over the Pacific Ocean. The missile fell to 8,000 feet before its rocket engine fired. The 10-second engine burn carried the missile to 20,000 feet again before it dropped into the ocean. The test proved the feasibility of launching an intercontinental ballistic missile from the air. Operational deployment was discarded due to engineering and security difficulties, though the capability was used as a negotiating point in the Strategic Arms Limitation Talks.
https://en.wikipedia.org/wiki/STRAT-Xhttp://www.cnn.com/travel/article/c5-galaxy-dover-museum-minuteman-missile/index.html
