Fire balloon A , or Fu - Go , was a weapon launched by Japan during World War II . A hydrogen balloon with a load varying from a incendiary to one antipersonnel bomb and four incendiary device s attached , they were designed as a cheap weapon intended to make use of the jet stream over the Pacific Ocean and wreak havoc on Canadian and American cities , forests , and farmland . The balloons were relatively ineffective as weapons but were used in one of the few attacks on North America during World War II . Between November 1944 and April 1945 , Japan launched over 9 , 300 fire balloons . About 300 balloon bombs were found or observed in North America , killing six people and causing a small amount of damage . Overview . From late 1944 until early 1945 , the Japanese launched over 9 , 300 of these fire balloons , of which 300 were found or observed in the U . S . Despite the high hopes of their designers , the balloons were ineffective as weapons : causing only six deaths ( from one single incident ) and a small amount of damage . Japanese bomb - carrying balloons were in diameter and , when fully inflated , held about of hydrogen . Their launch sites were located on the east coast of the main Japanese island of Honshū . Japan released the first of these bomb - bearing balloons on November 3 , 1944 . They were found in Alaska , Washington , Oregon , California , Arizona , Idaho , Montana , Utah , Wyoming , Colorado , Texas , Kansas , Nebraska , South Dakota , North Dakota , Michigan and Iowa , as well as Mexico and Canada . General Kusaba ' s men launched over 9 , 000 balloons throughout the course of the project . The Japanese expected 10 % ( around 900 ) of them to reach America , which is also what is currently believed by researchers . About 300 balloon bombs were found or observed in America . It is likely that more balloon bombs landed in unpopulated areas of North America . The last one was launched in April 1945 . Origins . The balloon campaign was the fourth attack the Japanese had made on the American mainland . The " fūsen bakudan " campaign was , however , the most earnest of the attacks . The concept was the brainchild of the Imperial Japanese Army ' s Ninth Army ' s Number Nine Research Laboratory , under Major General Sueyoshi Kusaba , with work performed by Technical Major Teiji Takada and his colleagues . The balloons were intended to make use of a strong current of winter air that the Japanese had discovered flowing at high altitude and speed over their country , which later became known as the jet stream . The jet stream reported by Wasaburo Oishi blew at altitudes above 9 . 15 km ( 30 , 000 ft ) and could carry a large balloon across the Pacific in three days , over a distance of more than . Such balloons could carry incendiary and high - explosive bombs to the United States and drop them there to kill people , destroy buildings , and start forest fire s . The preparations were lengthy because the technological problems were acute . A hydrogen balloon expands when warmed by the sunlight , and rises ; then it contracts when cooled at night , and falls . The engineers devised a control system driven by an altimeter to discard ballast . When the balloon descended below , it electrically fired a charge to cut loose sandbags . The sandbags were carried on a cast - aluminium four - spoked wheel and discarded two at a time to keep the wheel balanced . Similarly , when the balloon rose above about 11 . 6 km ( 38 , 000 ft ) , the altimeter activated a valve to vent hydrogen . The hydrogen was also vented if the balloon ' s pressure reached a critical level . The control system ran the balloon through three days of flight . At that time , it was likely over the U . S . , and its ballast was expended . The final flash of gunpowder released the bombs , also carried on the wheel , and lit a 19 . 5 meter ( 64 ft ) long fuse that hung from the balloon ' s equator . After 84 minutes , the fuse fired a flash bomb that destroyed the balloon . The balloon had to carry about of gear . At first the balloons were made of conventional rubberized silk , but improved envelopes had less leakage . An order went out for ten thousand balloons made of " washi " , a paper derived from mulberry bushes that was impermeable and very tough . It was only available in squares about the size of a road map , so it was glued together in three or four laminations using edible " konnyaku " ( devil ' s tongue ) paste . Hungry workers stole the paste and ate it . Many workers were nimble - fingered teenaged school girls . They assembled the paper in many parts of Japan . Large indoor spaces , such as sumo halls , sound stages , and theatres , were required for the envelope assembly . Similar , but cruder , balloons were also used by Britain to attack Germany between 1942 and 1944 . Offensive . Initial tests took place in September 1944 and proved satisfactory ; however , before preparations were complete , B - 29 s began their raids on the Japanese home islands . The attacks were somewhat ineffectual at first but still fueled the desire for revenge sparked by the Doolittle Raid . The first balloon was released in early November 1944 . Major Takada watched as the balloon flew upward and over the sea : " The figure of the balloon was visible only for several minutes following its release until it faded away as a spot in the blue sky like a daytime star . " The Japanese chose to launch the campaign in the beginning of fall , when the jet stream is strongest . This limited the chance of the incendiary bombs causing forest fires , as by that time of year , the forests were generally too damp to catch fire easily or covered in snow . The balloons continued to arrive in Oregon , Kansas , Iowa , British Columbia , Saskatchewan , Manitoba , Alberta , the Yukon , Northwest Territories , Washington , Idaho , South Dakota , Nevada ( including one that landed near Yerington that was discovered by cowboys who cut it up and used it as a hay tarp , another by a prospector near Elko who delivered it to local authorities on the back of a donkey , and another was shot down by U . S . Army Air Force planes near Reno ) . In all , seven fire balloons were turned in to the Army in Nevada , Colorado , Texas , Northern Mexico , Michigan , and even the outskirts of Detroit . Fighters scrambled to intercept the balloons , but they had little success ; the balloons flew very high and surprisingly fast , and fighters destroyed fewer than 20 . Among the U . S . units which fought the fire balloon was the 555th Parachute Infantry Battalion . The 555th suffered one fatality and 22 injuries fighting fires . By early 1945 , Americans were becoming aware that something strange was going on . Balloons had been sighted and explosions heard , from California to Alaska . Something that appeared to witnesses to be like a parachute descended over Thermopolis , Wyoming . A fragmentation bomb exploded , and shrapnel was found around the crater . A P - 38 Lightning shot a balloon down near Santa Rosa , California ; another was seen over Santa Monica ; and bits of washi were found in the streets of Los Angeles . In February and March 1945 , P - 40 fighter pilots from 133 Squadron , Royal Canadian Air Force operating out of RCAF Patricia Bay ( Victoria , British Columbia ) , intercepted and destroyed two fire balloons , On 21 February , Pilot Officer E . E . Maxwell While shot down a balloon , which landed on Sumas Mountain , in Washington State . On 10 March , Pilot Officer J . O . Patten destroyed a balloon near Saltspring Island , British Columbia . On March 10 , 1945 , one of the last paper balloons descended in the vicinity of the Manhattan Project ' s production facility at the Hanford Site . This balloon caused a short circuit in the power lines supplying electricity for the nuclear reactor cooling pumps , but backup safety devices restored power almost immediately . Two paper balloons were recovered in a single day in Modoc National Forest , east of Mount Shasta . Near Medford , Oregon , a balloon bomb exploded in towering flames . The Navy found balloons in the ocean . Balloon envelopes and apparatus were found in Montana , Arizona , Saskatchewan , in the Northwest Territories , and in the Yukon Territory . Eventually , an Army fighter managed to push one of the balloons around in the air and force it to ground intact , where it was examined and filmed . Japanese propaganda broadcasts announced great fires and an American public in panic , declaring casualties as high as 10 , 000 . Hayfork is a small community in northern California about 40 miles ( 65 km ) west of Redding . On February 1 , 1945 a Japanese bombing balloon was spotted by several local residents drifting over the Trinity National Forest area and slowly descending . No one knew what it was , but an alert forest ranger called the military authorities at the Presidio of San Francisco and reported it . Meanwhile the balloon came to rest atop a 60 foot ( 20 meter ) dead fir tree in the forest near a local road . In the next few hours several people gathered in the area to gaze up at the strange object . Shortly after dark there was a tremendous blast . The balloon ' s gas bag disappeared in a fireball and the balloon ' s undercarriage came crashing to the ground . No one was hurt . Forest rangers kept the curious well back from the fallen debris until Army personnel arrived . Upon examination , it was found to be a Japanese bombing balloon with four incendiary bombs and one high explosive bomb still aboard and the bomb releasing mechanism still very much intact . It later proved to be one of the most intact bombing balloons yet to fall into American hands . As was usual in instances of this sort , the local people were told what it was and were asked to keep secret what they had seen . Allied investigation . Despite their low success , the authorities were worried about the balloons . There was the chance that they might get lucky . Much worse , the Americans had some knowledge that the Japanese had been working on biological weapon s , most specifically at the infamous Unit 731 site at Pingfan in Manchuria , and a balloon carrying biowarfare agents could be a real threat . Nobody believed the balloons could have come directly from Japan . It was thought that the balloons must be coming from North American beaches , launched by landing parties from submarine s . Wilder theories speculated that they could have been launched from German prisoner of war camps in the U . S . , or even from Japanese - American internment centers . Some of the sandbags dropped by the " fusen bakudan " were taken to the Military Geology Unit of the United States Geological Survey for investigation . Working with Colonel Sidman Poole of U . S . Army Intelligence , the researchers of the Military Geological Unit began microscopic and chemical examination of the sand from the sandbags to determine types and distribution of diatom s and other microscopic sea creatures , and its mineral composition . The sand could not be coming from American beaches , nor from the mid - Pacific . It had to be coming from Japan . The geologists ultimately determined the precise beaches in Japan the sand had been taken from . By this time , it was mostly irrelevant , since by early spring the balloon offensive was almost over . Press coverup . The bombs caused little damage , but their potential for destruction and fires was large . The bombs also had a potential psychological effect on the American people . The U . S . strategy was to keep the Japanese from knowing of the balloon bombs ' effectiveness . In 1945 " Newsweek " ran an article titled " Balloon Mystery " in their January 1 issue , and a similar story appeared in a newspaper the next day . The Office of Censorship then sent a message to newspapers and radio stations to ask them to make no mention of balloons and balloon - bomb incidents , lest the enemy get the idea that the balloons might be effective weapons . Cooperating with the desires of the government , the press did not publish any balloon bomb incidents . Perhaps as a result , the Japanese only learned of one bomb ' s reaching Wyoming , landing and failing to explode , so they stopped the launches after less than six months . The press blackout in the U . S . was lifted after the first deaths to ensure that the public was warned , though public knowledge of the threat could have possibly prevented it . Japanese abandon the project . With no evidence of any effect , General Kusaba was ordered to cease operations in April 1945 , believing that the mission had been a total fiasco . The expense was large , and in the meantime the B - 29s had destroyed two of the three hydrogen plants needed by the project . The last fire balloon was launched in April 1945 . Single lethal attack . On May 5 , 1945 , a pregnant woman and five children were killed when they discovered a balloon bomb that had landed in the forest of Gearhart Mountain in Southern Oregon . Pastor Archie Mitchell and his pregnant wife Elsie drove up to Gearhart Mountain with five of their Sunday school students ( aged 11 – 14 ) to have a picnic , and Elsie and the children got out of the car at Bly , Oregon , while Archie drove on to find a parking spot . As Elsie and the children looked for a good picnic spot , they saw a strange balloon lying on the ground . As the group approached the balloon , a bomb attached to it exploded and Elsie and all five children were killed . Archie witnessed the explosion and immediately ran to the scene and used his hands to extinguish the fire on his wife ' s and the children ' s clothing , but he could not save them . These are the only known deaths caused by the balloon bombs , and also the only known deaths in the continental U . S . as the result of enemy action during World War II . Military personnel arrived on the scene within hours , and saw that the balloon still had snow underneath it , while the surrounding area did not . They concluded that the balloon bomb had drifted to the ground several weeks earlier , and had lain there undisturbed until found by the group . Elsie Mitchell is buried in the Ocean View Cemetery in Port Angeles , Washington . A memorial , the Mitchell Monument , is located at the point of the explosion , 110 kilometers ( 70 mi ) northeast of Klamath Falls in the Mitchell Recreation Area . It was listed in the National Register of Historic Places in 2001 . Several Japanese civilians have visited the monument to offer their apologies for the deaths that took place here , and several cherry trees have been planted around the monument as a symbol of peace . Post World War II . The remains of balloons continued to be discovered after the war . Eight were found in the 1940s , three in the 1950s and two in the 1960s . In 1978 , a ballast ring , fuses and barometers were found near Agness , Oregon and are now part of the collection of the Coos Historical & Maritime Museum .