Green Grass Yellow Sun (nuclear weapon)

a diagram of green grass warhead s steel ball safety device, shown left, filled (safe) , right, empty (live)

after green bamboo abandoned decision made use interim megaton weapon known green grass in yellow sun casing , designate yellow sun mk.1 until better warheads available mk.2. green grass of similar layout green bamboo, although not thermonuclear, being large unboosted pure fission warhead based in part on core of orange herald device tested @ grapple, of implosion , firing features of green bamboo. twelve green grass warheads fitted in larger, older casings derived blue danube , known violet club. these twelve warheads later transferred yellow sun mk.1 casings , supplemented further warheads totalling 37. green grass yield stated royal air force (raf) 500 kilotons of tnt equivalent (2.1 pj), designers estimate later revised downwards 400 kt of tnt. green grass warhead never tested. used dangerously large quantity of fissile material – thought in excess of 70 kilograms (150 lb), , considerably more uncompressed critical mass. kept subcritical being fashioned thin-walled spherical shell. guard against accidental crushing of core critical condition, shell filled 133,000 steel ball-bearings, weighing 450 kilograms (990 lb). in conflict, these have had removed before flight. raf thought unsafe.