Type 99 No.3 Mk.3 Sango (IJN)

Designed in 1938 and entering service in 1939, this anti-bomber bomb contained 144 white phosphorous-filled steel pellets. Its tail fins were offset to impart spin as it fell and this armed the tail fuse. The fuse would then trig­ger a burster tube down the middle of the bomb, scattering the pellets. A charge in the tail ensured the pellets were directed down­wards. Should the tail fuse fail, an impact fuse was proved in the nose of the bomb. A later modification of the bomb added fins to the body to impart a faster spin. For identification purposes the nose of the bomb was painted silver and the fins red. The bomb was.7m (2.3ft) long and weighed 34kg (741b).

Ro-Ta (IJA)

One of the problems the Japanese had with using cluster munitions was that they relied on the attacker having a higher altitude than the target in order to rain the bomblets down upon them. However, many Japanese fighters struggled at the altitudes at which the B-29s usually operated. The IJA sought to solve this dilemma with the Ro-Ta. The same Та bomblets were used but the canister was essentially a rocket that was launched towards the target. A timed fuse would trigger an explosive charge that scattered the Та bomblets. In effect, the Ro-Ta was like a buck­shot shotgun shell. Because the Ro-Ta could be fired like a rocket, there was no longer a requirement to be above the intended target in order to use the weapon. Luckily for the Allies, the Ro-Ta was still in development when the war ended.

To-2 (IJA)

Even before the To-З and Та series of cluster bombs, there was the To-2 parachute bomb. Developed in 1935, the To-2 was a 1.8m (41b) bomb that was suspended from a length of steel cable that was itself connected to a silk parachute. Ten To-2 bombs were clustered together, each cluster weighed 50kg (1101b) and the average single engine fighter could carry up to four clusters. The usual tactic was to drop the To-2 bombs into the path of oncoming bombers. To increase the depth of the bomb spread, some To-2 bombs had a smaller parachute that would result in a faster descent. The bomb was armed with an impact fuse that, regardless of where the bomb struck, would trigger the detonation. Usually the cable would be hit by the bomber with the bomb swinging up and against the plane, exploding the bomb. The To-2, how­ever, was not developed further because the cable was typically cut if hit by a wing, it relied on a high altitude to be effective and the Та munition showed far greater promise.

Japan was able to achieve where Germany failed and that was to bomb the US mainland. On 9 September 1942, the Japanese subma­rine 1-25 surfaced west of Cape Blanco, Ore­gon, and a single Kugisho E14Y1 floatplane (known as Glen to the Allies) was assembled. Pilot Warrant Officer Nobuo Fujita and observer Petty Officer Okuda Shoji climbed into the plane that was loaded with two 77kg (170 lb) incendiary bombs and took off for the US coast, heading towards the Oregon side of the Siskiyou National Forest. Once over the forest, the bombs were released in the hope a forest fire would start. However, recent rains coupled with the bombs having been dropped too low resulted in a few small fires and these quickly put out. The attack would be repeated again on 29 September 1942 but once more the results were disappointing. The first attack marked the only time in history an enemy aircraft bombed the US but another plan was in the works, one far more ambitious and ingenious, but ultimately fruitless.

The plan was called the Fu-Go, ‘Fu’ being the first kanji of the word ‘fusen’, meaning bal­loon. The ‘Go’ simply meant type. Originally conceived in 1933 by Lieutenant General Rei – kichi Toda of the Japanese Military Scientific Laboratory, the bomb dropping balloon Fu-Go was part of a series of studies into possible new weapons. Experiments with balloons capable of maintaining a stable altitude were initially allowed to proceed but by 1935 the Fu – Go project was cancelled. However, following the famous Doolittle raid on 8 April 1942, the Fu-Go was revived as a means of exacting ret­ribution for the attack.

The Fu-Go was to have been launched from submarines situated 998km (620 miles) off the US coast. In March 1943, a 6.1m (20ft) diameter balloon was successfully launched and remained aloft for at least ten hours, enough to make the submarine launch plan work. The main problem was the effect of temperature on the hydrogen gas used in the balloon. At night and in cool temperatures, the gas pressure was reduced and the balloon lost buoyancy while by day, in higher tempera­tures, there was the risk of the gas expanding and rupturing the gas envelope. Because of this launches of the balloons had to take place either by day or by night and not straddle the two times of day. However, the UN’s need for submarines to support operations in the Pacific left no room for launching the Fu-Go and the project was again cancelled in August

1943.

Remaining undeterred, the Fu-Go engi­neers looked into a solution where the bal­loon could be launched from Japan, although it would now take 50-70 hours for it to traverse the Pacific Ocean and arrive over the US mainland. General Sueyoshi Kusaba was put in command of the project to tackle the dis­tance issue and put the Fu-Go into operational use.

To overcome the problem of maintaining altitude as the balloon travelled by day and night, a ballast mechanism was designed. This consisted of a cast aluminium ring around which 32 2.5 to 3.2kg (5.5 to 7 lb) sand­bags were secured. Fuses were fitted to pairs of sandbags, the fuses powered by a small battery and connected to aneroid barometers. When the balloon sank to an altitude of around 9,144m (30,000ft), the aneroid barom­eter would trigger a switch. In turn, this trig­gered a fuse which in turn would fire two small charges that would each release a sand­bag, one across from the other to maintain balance. The balloon would then rise to an altitude of around 11,582m (38,000ft) where a gas release valve set into the bottom of the envelope discharged some of the gas to keep the balloon from rising higher. Eventually it would drop again triggering another release of sandbags followed by a rise, vent and the cycle would repeat. By the time the last pair of sandbags was dropped, it was estimated that the balloon should be over the US mainland where its destructive payload would then be released.

The balloon could lift a maximum of 136kg (3001b) at 9,144m (30,000ft). The typical munition payload was one Type 92 15kg (33 lb) high explosive bomb, one Type 100 5kg (11 lb) incendiary bomb and one Type 97 12kg (26.4 lb) incendiary bomb. A 29m (64ft) fuse was connected to a charge on the gas enve­lope and once the bombs were dropped, the fuse was lit which, in turn, destroyed the balloon.

The spherical gas envelope could store 538m3 (19,000ft3) of hydrogen gas. The diame­ter at full inflation was 10m (33ft). Early gas envelopes were constructed from rubberised silk but this was too costly to construct and the production Fu-Go used Washi paper made from the kozo bush. While Washi was inex­pensive and already produced by hand in paper mills across Japan, there was no means to ensure a constant level of quality. There­fore, the Fu-Go program had to develop mechanical methods to make Washi as well as laminate it. It took four to five layers of Washi to make a gore (a segment) and 38 to 64 gores glued together to make the sphere. The adhesive used, called konnyaku-nori, was made from konnyaku, a potato. As the glue was relatively clear, colouring was added so workers could check for evenness in the application. The glue also served as a sealant to prevent gas leakage as the untreated Washi was porous.

After being brushed with the glue, each gore was inspected for flaws. This was done by laying the gores over a panel of frosted glass beneath which was a light. The glue would appear blue and any uneven applica­tions of the glue showed up as a lighter area. All flaws were marked and patched. Once the gores had passed inspection, they were taken to the final assembly area. A large room was required with sharp objects padded so not to rip the gas envelope. High school girls were often employed for assembly, using the glue to affix the gores together to create the com­pleted gas envelope. Each girl had to ensure her nails were trimmed, that she wore gloves and socks, and that she did not wear hair pins as these could damage the gas envelope. Once the envelope was finished, it was taken to another building, often a sumo hall or the­atre (buildings specific for the task were later built), and inflated to check for leakage. After successfully passing the final inspection, the Fu-Go was completed.

The finished Fu-Go had a scalloped waist­band around the gas envelope to which the 19 shroud lines, each 14m (45ft) long, were secured. The lines were brought together and tied into two knots from which the bombs and the ballast system were hung.

With the problem of keeping a relatively sta­tic altitude solved, the next hurdle was to determine where and when to launch the bal­loons. Towards the close of 1943 and into the early part of February 1944, the Japanese launched balloons equipped with radios which were tracked so their courses could be monitored. Two stations set up in Hokkaido and in Chiba Prefecture could track the bal­loons only through the first portion of their flight, but once over the open ocean all con­tact was lost. The Japanese were aware that the west-to-east wind speeds were at their peak from November through to March, top­ping out at 298km/h (185mph). In addition, a shortage of meteorological data on weather patterns over the ocean and at high altitudes limited the ability to plan trajectories for the balloons. While the winds were higher, it was also winter throughout most of the launch window. In addition, the balloons had to be released in clear, cloudless weather with little surface wind. If balloons were sent up in over­cast skies with precipitation laden clouds, moisture would collect on the balloons which would freeze at higher altitudes, adding weight resulting in the balloons being unable to reach the US. Three major launch sites were selected: Nakoso (Fukushima Prefec­ture), Otsu (Ibaraki Prefecture) and Ichin Omiya (Chiba Prefecture).

On 3 November 1944, the Fu-Go balloon bombing campaign was officially opened. In all, between 9,000-10,000 balloons were avail­able and by 20 November, the first en masse launchings had taken place. Prior to launch, the sandbag release mechanism was set based on the estimated wind speeds to ensure the balloon was over the US before releasing its payload. The gas envelope was only partially filled to allow for expansion of the hydrogen at an altitude of 4,877m (16,000ft). On a good day crews could launch up to 200 balloons. March 1945 would see the highest number of balloons deployed, 3,000 in all, and the final launch was made on 20 April. Typically included in batches of balloon launches would be a radio equipped balloon to allow for tracking.

The first balloon was found on 4 November 1944 by a US Navy patrol boat. It had crashed into the sea 106km (66 miles) southwest of San Pedro, California. Nothing much was made of it until another turned up in the sea two weeks later. Also, balloons were found up in Montana and Wyoming and the US military realised the purpose of the balloons. Federal and state agencies were put on alert (espe­cially forest services as the threat of forest fires from the incendiaries was very real) and steps were taken to prevent news of the balloon bombs reaching the general public. This was done to prevent panic in the populace since no one could be sure when or where a bal­loon would release its bombs. In addition, by keeping the story from the press, the Japanese would be denied any information on the effectiveness of their attacks. The censorship was very effective and only one story con­cerning a balloon bomb was published appearing in Thermopolis in Wyoming. This was also reported in a Chinese newspaper. From this, the Japanese judged the Fu-Go campaign was a success and the balloon campaign continued.

The near total shutdown of public informa­tion on the balloon bombs had one severe drawback for the Americans and that was that the public had no knowledge of their exis­tence and consequently were not be warned of the dangers. The censorship would be reversed after an inevitable tragedy occurred. On 5 May 1945, near Bly, Oregon, Reverend Archie Mitchell, his wife and five children from his church group were enjoying a picnic in a wooded area. One of the children, Joan Patzke, found a balloon stuck in a tree and tried to pull it down. The subsequent explo­sion of the bombs it carried killed all but Rev­erend Mitchell. The deaths would be the only US mainland casualties from enemy action. Following the incident, the censorship was lifted to ensure public safety.

The Fourth Army Air Force was tasked with the detection and interception of the balloons. In addition, Project Firefly was initiated to position aircraft and troops to respond to for­est fires. Project Lightening was set up through the Department of Agriculture to be on alert for biological attacks against crops and livestock. Successful interception of the balloons proved difficult owing to the high alti­tudes at which they travelled, poor ground reporting and inadequate weather reporting (this would also hamper the ability of the US to accurately determine launch points from Japan). In fact, only two Fu-Gos were shot down over the US mainland. Only US Army and US Navy assets in the Aleutian Islands had a higher tally as the balloons often passed over the territory. With the problems in locating the balloons, a final plan, Project Sunset, was ini­tiated to create a web of radar sites across the coastline of Washington State. When balloons were detected, interceptors would be scram­bled to engage them. As it turned out, the plan was put into action in April 1945, the same month the Japanese ceased launching the Fu – Go. In any case, radars had a difficult time in detecting the balloons due to their low signal return.

The cost to produce one Fu-Go was approx­imately 10,000 yen. If the added expense of the design and production of the mechanical equipment to produce Washi and the erec­tion of buildings to inspect the balloons, the price of the Fu-Go project was high in com­parison to the results it brought. Still, Japanese propaganda broadcasts played up the Fu-Go prior to the project being cancelled in April 1945.

Ironically, on 10 March 1945, a balloon from one of the last launchings struck a power line, resulting in the loss of power to the nuclear plant in Hansford, Washington. This plant cre­ated the atomic material used in the Manhat­tan Project’s atomic bombs, which would ultimately be used against Japan. The loss was barely noticed as back-up systems came online to maintain the reactor. Another irony occurred on 13 March 13 when two Fu-Gos returned to Japan, although they touched down without causing any damage.

In all, 296 balloon sightings or incidents were reported across 17 US states, 5 Canadian provinces and Mexico out of the 9,000-10,000 launched. Hundreds remain unaccounted for and even today, some may still lurk in unpop­ulated areas or in dense forest presenting a danger to anyone encountering one.

Interestingly, the British would use a similar weapon against Germany. Called Operation Outward, hydrogen filled balloons equipped with a trailing steel chain to short out power lines and three 6 lb incendiary devices to trig­

Appendix