05 December 2010

The Japanese Balloon Offensive of 1944-1945

On 18 April 1942, the Doolittle Raid on Japan not only provided a tremendous boost to American morale but it spurred the Japanese military to search for a way to exact revenge in the form of retaliatory attacks on the American homeland. Following the defeat at Midway, some in the Japanese military command realized that it was only a matter of time before the Home Islands would come under air attack yet no means existed for Japan to reach the North America which would remain untouched. An interim measure was evaluated that used Yokosuka E14Y (Allied code name "Glen") reconnaissance seaplanes launched for submarines to attack US targets- one such attack did take place on 9 September 1942 when a Glen floatplane was launched from I-15 in a failed attempt to ignite forest fires using incendiary bombs near Brookings, Oregon. Improved designs were being planned for submarine deployment off the US West Coast, but the Guadalcanal campaign in the Solomon Islands required every available Japanese submarine pressed into service to make clandestine supply runs to forces on the island. One-way attacks using long-range land-based bombers were considered, but there were no suitable airfields within range of the United States. It was at this time that a pre-war weapons concept using balloon-borne bombs was reconsidered for use. 

In 1933 the Japanese Military Scientific Laboratory was assigned the task of developing new and novel weapons. One design extensively studied was called the "Fu-Go" weapon; "Fu" being the first Japanese character of the word for balloon (fusen) and "Go" representing a type number. Experiments were conducted on how to get a hydrogen-filled balloon to maintain a constant altitude, but the Fu-Go" project lost priority to focus on more promising technologies. Low-level work did continue on the Fu-Go weapon and priority was given back to the program following the Doolittle Raid with the testing of a 20-foot balloon with a 10-hour endurance that could be launched from a submarine. The relatively short endurance was to limit the effects of diurnal heating on the balloon, allowing it to maintain a constant altitude, but it required the submarine to surface no more than 600 miles off the US West Coast. However, like the submarine floatplane projects, it was shelved due to the need for Japanese submarines during the battles for Guadalcanal in the southwest Pacific. The only option for the Fu-Go weapon was a launch from Japan, but this entailed a flight time of 50-70 hours and some way was needed to maintain a constant altitude despite the effects of heating and cooling with the diurnal cycle. Expansion in the daytime would cause the balloon to rise and as the gas expanded, the balloon would burst. Cooling at night caused gas contracting and altitude loss. 

The solution was to incorporate a pressure release valve at the base of the balloon to offset daytime heating and a cast aluminum wheel suspended below the balloon that not only carried the bomb payload, but the wheel perimeter had a series of approximately 32 attachment points to which sandbags were attached that could be released by detonating a small squib triggered by a barometer that was preset to a certain altitude. As the balloon rose, the valve was set to open a particular pressure, keeping the balloon at approximately 38,000 to 40,000 feet where prevailing winds could carry it eastward to North America. At night, the barometer was set to approximately 30,000 feet. Triggered by a battery and barometer, two sandbags could be dropped that allowed the balloon to rise again up to the desired altitude. Once all the sandbags had been dropped, the bomb load (usually two incendiary bombs and a single high explosive bomb) was released and the balloon self-destructed. Preliminary tests in the winter of 1943 with radio-tracked balloons first revealed what we now know as the jet stream- at the time there was no knowledge of the upper level winds that existed above 40,000 feet. This was something that American Boeing B-29 Superfortress crews would discover as well in the same time frame. As the upper wind studies continued in the early part of 1944, launch sites and manufacturing sites were being prepared. Three major launch sites were constructed on the east coast of Honshu, the main island where Tokyo and most of Japan's industry was located. Radio direction finding stations were also set up as a radio-tracking balloon would be released with each group. 

The balloons needed to be made of a gas-proof material that was made of a non-critical material which ruled out rubber. It was found that tissue paper made from the mulberry tree worked well. Four to five layers of tissue paper were used which were sealed with an adhesive made from potatoes called konnyaku. The adhesive was tinged with blue coloring so the application and thickness of the colorless adhesive could be seen. At a time when there were numerous food shortages in Japan as the American submarine blockade of the Home Islands intensified, it wasn't unusual for balloon workers to steal the raw powdered konnyaku to use at home as flour. Once laminated with the adhesive paste, gores were cut to form the balloons and more of the paste was used to adhere one gore panel to the next, with 38 to 64 panels used to form a balloon that was approximately 33 feet in diameter that could hold 19,000 cubic feet of hydrogen gas. Fully inflated, the balloon could lift 1,000 lbs. A scalloped shroud along the balloon's circumference carried the lines to the payload gondola that held the bombs and the sandbags. As buildings with large interior open spaces were needed to test the balloons for leaks, music halls, auditoriums and even sumo wrestling arenas were pressed into service for the balloon offensive. 

General Sueyoshi Kusaba was placed in charge of the offensive and he figured that he had about five months to prove that the Fu-Go weapon could work. He was allocated 10,000 balloons but the balloons could only be launched on cloudless days with little wind. Rain, snow, or clouds could cause moisture on the balloons that would weight them down and prevent them from reaching their operating altitude. He had determined that in the assigned five-month period, he would have only fifty days to launch balloons and that meant launching approximately 200 balloons from the three launch sites each of the favorable days. With the American public aware of the German V-2 offensive in Europe at this time, it was thought that the balloon offensive would have its maximum impact on the US population that had already seen the effects of kamikaze attacks on the Pacific Fleet on newsreels. The first balloons were launched on 3 November 1944 at 0500 to much fanfare. It happened to be the birthday of the Emperor Meiji, who reigned over Japan during its transformation from fuedal state to industrial power at the turn of the century. Many in Japan saw this as a good omen at a time when the first Superfortress missions began their rain of destruction on the Home Islands from bases in China and the Marianas Islands. 

Two days later, a US Navy patrol boat spotted a large tattered cloth attached by lines to metal device 66 miles southwest of Long Beach, California. The debris was hauled aboard for analysis and was determined to be some sort of balloon. Ironically, this balloon was from the first group launched on 3 November. No particular significance was attached to the recovery until two weeks later when a second balloon was salvaged off the coast of California. Within four weeks balloons were recovered from Wyoming and Montana. Cognizant of the possibility of a new weapon, the military summoned government agencies at all levels and forest rangers were asked to report any balloon landings or recoveries of any of the metal gondolas. Though not confirmed at that point in the balloon offensive, it was assumed the devices were Japanese in origin as the prevailing winds were known to be from the west. Great importance was placed on the possible psychological reaction of the American public and some in the intelligence apparatus of the US military were aware of Japanese biowarfare experimentation in Manchuria at the infamous Unit 731. Could the balloons be used to spread biological disease? Agricultural laboratories across the western United States were asked to be on the lookout for any unusual clusters of crop or livestock disease. Medical authorities as well were alerted to be on the lookout for any unusual communicable disease outbreaks. The government at the time feared the consequences of a general panic. When press reports came out about the discovery of a balloon weapon near Thermopolis, Wyoming, the government asked for the cooperation of the press in self-censoring any stories about the balloons to prevent a general panic.

In December 1944, a Chinese newspaper published accounts of a balloon weapon discovered in the United States. This gave General Kusaba renewed effort to continue with balloon offensive and he instructed his staff to screen American, Russian and Chinese news reports for any accounts of balloons in the United States. As more of the balloons were being reported now that the US military had established a framework in fighting the  balloons, the Fourth Air Force of the US Army Air Force, headquartered at Hamilton Army Air Field in California, was placed in charge of US continental air defense efforts. Given that the risk of a Japanese air attack had diminished considerably by 1944, most of the Fourth Air Force's duties at the time focused on flight training for the war effort. It was determined based on what had been recovered so far that the biggest threat by the Japanese balloons would be the forest regions of the West during the dry season. Under Project Firefly, Stinson L-5 spotter planes and Douglas C-47 transports along with nearly 3,000 troops were deployed as rapid deployment forest fire-fighting teams at various points in the western states. Airborne paratroopers trained as smokejumpers also were deployed. Project Lightning was established to defend against the possibility of the balloons carrying biowarfare agents. Decontamination chemicals and sprays were stockpiled throughout the western states as well as the US Department of Agriculture advised health and agricultural laboratories, veterinary colleges and medical schools to be on watch for any usual disease outbreaks. 

The first interception attempt by fighter aircraft was made on 19 December 1944 when four fighters were scrambled from Santa Monica, California, to search for a reported balloon. Between 1 December 1944 and 1 September 1945, over 500 aircraft sorties were flown in search of reported balloons, but only twice did US-based fighters actually intercept a balloon. The first interception took place on 23 February 1945 by a Lockheed P-38 Lighting scrambled from Santa Rosa Army Air Field (now Sonoma County Airport) that shot down a balloon near Calistoga, California. The second interception occurred on 22 March 1945 when a balloon spotted over Redwood, Oregon was tailed all the way to Reno, Nevada. As the balloon finally settled in the mountains near the city, a determined USAAF pilot landed and continued his pursuit by car, wanting to make a capture of an intact balloon. As the balloon dragged along the ground, some ballast got released and it rose up again and headed upward again only to be finally shot down by a Bell P-63 Kingcobra. More success came to fighters based in Aleutian Islands- as most of the balloons passed over this area, both USAAF and Navy pilots fared better. On 13 April 1945 alone, Navy Grumman F6F Hellcats shot down nine balloons at altitudes between 30,000 to 37,000 feet, at the service ceiling for the fighter. At the time, the shootdown of that many balloons was thought to reflect an increased tempo in the balloon offensive, but the general lack of press reports due to the self-censorship of the American media led to the end of the balloon offensive that same month. Two of the three hydrogen plants also used in the offensive had been destroyed by B-29 attacks as well. Not knowing this, the US began Project Sunset that month with the set up of radar sites along the Washington coast. The radar sites would search, detect, and track the balloons. This information was then passed to alert fighters (Lockheed P-38 Lightnings and Northrop P-61 Black Widows) positioned at Paine Field in Everett, Washington, north of Seattle, and a naval auxiliary field outside of Shelton, Washington, south of Seattle. Despite numerous sighting reports, Project Sunset detected not one single balloon as the Japanese had stopped launching the Fu-Go weapons. Sixty-eight times, though, fighters were scrambled based on visual reports, but they all ended up being either weather balloons, Navy blimps, or even the planet Venus.

Despite the end of the balloon offensive in April 1945, on 5 May 1945, a pregnant woman and five children were killed outside of Bly, Oregon in the southern part of the state. A church pastor, Arnie Mitchell, and his pregnant wife, Elyse, were taking five Sunday school children on a picnic. As he searched for a parking spot, Elyse and the students found a Fu-Go balloon on the ground. As they approached it, a bomb still attached to it exploded. They are the only deaths of the balloon offensive and the only deaths in the continental United States due to enemy action in the Second World War. A monument in the town today to the victims is surrounded by cherry trees planed by Japanese visitors as a symbol of apology and peace. Of the 10,000 balloons launched, they were found as far east as Michigan and as far south as Texas and northern Mexico. In the five years after the end of the war, eight more were found, three in the 1950s, and two in the 1960s. In 1978 a gondola with its barometer, some of the squibs and ballast was found in Oregon. 

Ironically some of the recovered ballast was turned over the US Military Geology Unit to determine the origin of the balloons. At the time it was thought that perhaps the balloons were being launched from submarines that were landing clandestine units at night on the beaches for the US coast. By studying the sand under microscope for diatoms and a chemical analysis of the minerals in the sand, the geologists were able to rule out any North American beaches as the source of the sand. The diatom species present allowed them to determine the precise Japanese coastal launch sites for the balloons, but by the time that determination had been made, the balloon offensive had ended. 

Source: Air Enthusiast International, February 1974, Volume Six. "Bombs by Balloon" by Robert C. Mikesh, p75-83.


  1. This blog is really a great blog to visit daily i like to read the posts on this blog it is very much useful in our career i want to subscribe the blog so can you give the subscription details and tell me when your blog gets updated.

  2. Informative and mind boggling as well ! Good job.

  3. Great blog! My dad told us stories about these ballons many times. He was a radar repair tech and was at Paine Field in Everett, Washington with the P-61'S that were there to intercept these ballons. The part about the planes chasing the planet Venus thinking it was a ballon was true, he told us that too!