Tsar Bomba
During its operational lifetime, the B-41 was the most efficient known thermonuclear weapon in terms of yield to actual weight, with a ratio (based on a yield). Its blast yield was to that of the "AN602 Tsar Bomba", which delivered a blast of , depending on its own configuration as a "clean" (lead encased) or "dirty" (uranium encased) bomb. However even at the "Tsar Bomba's" theoretical maximum yield of , it would still only achieve a yield to weight ratio of ~ , thus the B-41 is the most efficient, highest yield to weight ratio, weapon ever created. However, since neither full yield versions of the B-41 nor "Tsar Bomba" were ever demonstrably tested, the B-41's high efficiency is merely theoretical; the most efficient tested and proven nuclear physics package is the W56.