WASHINGTON – North Korea's overt threat to launch a pre-emptive nuclear strike against the United States is unprecedented in its bluntness. But other nuclear powers, including the United States, have made less explicit threats. Here are some examples:
— November 1950: U.S. President Harry Truman, the only leader to ever order a nuclear strike, said in a press conference that the use of atomic weapons was under "active consideration" in the Korean War against targets inside China. The White House later clarified that that the comment was theoretical, noting that "consideration of the use of any weapon is always implicit in the very possession of that weapon."
— March 1955: After China's People's Liberation Army seized a group of islands in the Taiwan Strait during the first Taiwan Strait Crisis, U.S. Secretary of State John Foster Dulles said the U.S. could intervene with nuclear-equipped ships and planes under some circumstances.
The next day, U.S. President Dwight Eisenhower said he saw no reason why nuclear weapons "shouldn't be used exactly as you would use a bullet or anything else." To make sure China got the point, a day later then-Vice President Richard Nixon said that "tactical atomic weapons are now conventional and will be used against the targets of any aggressive force."
— July 2005: Chinese Maj. Gen. Zhu Chenghu said that China might retaliate with nuclear weapons if the United States attacked Chinese forces in a conflict over Taiwan. The Chinese government later played down the comments saying they were the personal views of the general, then a dean at the country's National Defense University.