Fangataufa kiloton Breusch W49 Pokhran 25QppQpp0 WEQp177 megaton B61 W68 B57 Plowshare W28 weapon Enewetak W44 B83 Gundremmingen W70 snRNAs weaponization thermonuclear W88 HNF4 121m Maralinga WEQp177A Gerboise Brahmastra 36H SLBM detonations Moruroa Nuncia W91 oconnori Hardtack exoatmospheric