The Tsar Bomba was the single most physically powerful device ever deployed on Earth. For comparison, the largest weapon ever produced by the U.S., the now-decommissioned B41, had a predicted maximum yield of . The largest nuclear device ever tested by the U.S. (Castle Bravo) yielded because of an unexpectedly high involvement of lithium-7 in the fusion reaction; the preliminary prediction for the yield was from . The largest weapons deployed by the Soviet Union were also around (e.g., the SS-18 Mod. 3 warhead).