 Whereas the lowest selectable yield of a tactical B61 (Mod 3 and Mod 4) is 0.3 kilotons (300 tons), modern PAL mechanisms ensure that centralised political control is maintained over each weapon, including their destructive yields.With the introduction of the B61 Mod 12, the United States will have four hundred identical nuclear bombs whose strategic or tactical nature will be set purely by the mission and target as well as type of aircraft on which they are carried.According to several reports, including by the Carnegie Endowment for International Peace and Bulletin of the Atomic Scientists, as a result of the effectiveness and acceptability of USAF use of precision munitions with little collateral damage in the Kosovo conflict in what amounted to strategic destruction once only possible with nuclear weapons or massive bombing, Vladimir Putin, then-secretary of Security Council of Russia, formulated a concept ("“escalate to de-escalate”") of using both tactical and strategic nuclear threats and strikes to de-escalate or cause an enemy to disengage from a conventional conflict threatening what Russia considers a strategic interest.