F-100D-60-NA (sn 56-2904) in trial of zero-length-launch system. Pilot is Maj. R. Titus (USAF photo).
The zero-length launch system or zero-length take-off system (ZLL, ZLTO, ZEL, ZELL) was a system whereby jetfighters and attack aircraft were intended to be placed on rockets attached to mobile launch platforms. Most zero length launch experiments took place in the 1950s, during the Cold War.
The primary advantage of a zero-length launch system is the elimination of the need for a vulnerable airfield for takeoffs. In the event of a sudden attack, air forces could field effective air defenses and launch airstrikes even with their own airbases destroyed. Although launching aircraft using rocket boosters proved to be relatively trouble-free, zero length launch systems still required a conventional runway if the aircraft was expected to land. Bulky mobile launching platforms also proved to be expensive to operate and difficult to transport. Security would also have been an issue with mobile launchers, especially if equipped with nuclear-armed strike fighters.
The United States Air Force, the Bundeswehr'sLuftwaffe, and the Soviet Air Force all conducted experiments in zero-length launching. The first manned aircraft to be ZELL was an F-84G in 1955. The Soviets main interest in ZELL was for point defense air defense of airfields and critical targets using Mig-19s. All works upon ZELL aircraft were abandoned due to logistical concerns and the increasing efficiency of guided missiles.