The deaths were all caused by a fire balloon (or balloon bomb), an unconventional weapon launched by Japan during World War II. A hydrogen balloon with a load varying from a 15 kg (33 lb) anti-personnel bomb to one 12-kilogram (26 lb) incendiary bomb and four 5 kg (11 lb) incendiary devices attached, it was designed as a cheap weapon intended to make use of the jet stream over the Pacific Ocean and drop bombs on American and Canadian cities, forests, and farmland. The bombs proved largely ineffective, but their potential for destruction and fires was large; they also had a potential psychological effect on the American people. The U.S. strategy was to impose a news blackout of this potential threat: the Office of Censorship sent a message to newspapers and radio stations to ask them to make no mention of balloons and balloon-bomb incidents. They did not want the enemy to get the idea that the balloons might be effective weapons or to have the American people start panicking. However, on May 5, 1945, Elsie Winters Mitchell and five children were killed when they discovered a balloon bomb that had landed in the forest of Gearhart Mountain in Southern Oregon. These are the only known deaths caused by the balloon bombs and the only known deaths in the contiguous U.S. as the result of enemy action.

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