The quarantine began on 24 October and tensions mounted as the Soviets continued to work on the missile sites and their ships continued moving toward Cuba. Then on 26 October, Khrushchev sent another message in which he offered to withdraw or destroy the weapons in Cuba, provided the United States would lift the blockade and promise not to invade the island. The increasing tempo in the military, however, continued unabated. SAC ordered over sixty B-52 bombers to continue on airborne alert, while TAC forces in Florida assumed a one-hour alert and prepared to go to a fifteen-minute alert, which involved pilots waiting in aircraft for launch orders.