The RAF's V-bomber force consisted of three high peformance strategic bombers, the Valient, Victor and Vulcan forming the United Kingdom's strategic nuclear strike force duing the 1950s and 1960s. Under the Quick Reaction Alert (QRA) system, the aircraft could be scrambled in under 2 minutes in response to an attack. This was made possible using a system called Mass Rapid Startup which allowed the entire aircraft and all 4 engines to be started with one button. The Vulcan was armed first with the fission weapon Blue Danube, superseded by the thermonuclear Yellow Sun.