The Tsar Bomba is the single most physically powerful device ever used by mankind.[12] By contrast, the largest weapon ever produced by the United States, the now-decommissioned B41, had a predicted maximum yield of 25 megatonnes of TNT (100 PJ), and the largest nuclear device ever tested by the United States (Castle Bravo) yielded 15 megatonnes of TNT (63 PJ), due to an unexpectedly high involvement of lithium-7 in the fusion reaction; the preliminary prediction for the yield was from 4 to 6 megatonnes of TNT (17 to 25 PJ). The largest weapons deployed by the Soviet Union were also around 25 megatonnes of TNT (100 PJ), as in the SS-18 Mod. 3 ICBM warheads.