What I heard about the Tsar Bomb (from wikipedia?) was that A) the name was probably given by the CIA since it's doubtful the commies would have named anything 'Tsar' and B) that they decreased the power of the bomb since a 100 Megaton would have thrown so much fallout into the atmosphere that it would have circled the northern hemisphere for quite some time and made relations with the other nations in the northern hemisphere even more tense than they already were.