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The Japanese Balloon Bomb Assault on North America: An Alberta Perspective

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N. Frank Chiovelli

Reprinted with permission of the author and publisher of For King and Country: Alberta in the Second World War

For King and CountryJapan's surprise attack on Pearl Harbor early on the Sunday morning of 7 December 1941 shocked the world and drew the United States of America into the Second World War. Simultaneous attacks arcing across the Pacific Ocean through Midway, Guam, Wake Island, Hong Kong, the Philippines, Malaya and Thailand soon resulted in victory over this huge area by Japan's armed forces. Coupled with huge losses meted out by Nazi Germany and her Axis partners in Europe and North Africa, the population of the Allied countries was thunderstruck. The series of military defeats on all fronts was a serious blow to their morale; an Allied military success was needed quickly to restore confidence.

The United States Navy and the US Army Air Force cooperated in training a squadron of B-25 bomber crews to fly from aircraft carriers. This squadron was put aboard the USS Hornet and sailed for the South Pacific. Off the coast of Japan, being discovered by Japanese picket boats, the Hornet launched her B-25s under the command of Lieutenant Colonel James A. Doolittle on 8 April 1942, successfully carrying out the first air raid on the Japanese home islands. News of this air raid immediately raised morale throughout all of the Allied nations.

Shock reverberated throughout Japan. The Imperial Japanese Navy understood the severe threat to their supply lines caused by the Doolittle Raid and sought out the US Fleet. This action ultimately led to the pivotal battle of Midway. When the US Fleet won the Battle of Midway it began a chain of military reversals that led to the final defeat of Japan on 14 August 1945, and the formal surrender on 2 September 1945.1

The Japanese military were forced to seek alternative ways to bolster the morale of its civilian population. It did not have long-range bombers that were capable of reaching the continental United States. Aircraft that could make such a one-way flight were still on the drawing board. The 9th Military Technical Research Institute [MTRI], after conferring with meteorologist Mr. H. Arakawa, decided that using balloons to mount a bombing attack on the North American continent could accomplish its goal and provide an immediate face-saving opportunity for the military. Arakawa had access to wind current information from civilian forecasting agencies, and from balloon experiments initiated in 1933 by the 9th MTRI [Tokyo], and the infamous Unit 731 in Manchuko [Manchuria]. Established during the Sino-Japanese War, Unit 731 had carried out medical experiments using imprisoned civilians and POWs as guinea pigs. This unit also had conducted experiments using balloons as delivery vehicles for biological warfare agents, and even as a possible method of transporting foot soldiers behind Chinese lines. Balloons used by both establishments were small, having a diameter of 4 metres [13.1 feet], and were designed to fly at a constant altitude for a distance of about seventy miles. Timing fuses were designed to release the bomb loads. However, work on these projects was never completed, and they were stopped in 1935.2

Japan trained an elite parachute force at this time, and the tactical advantage of that fighting unit far outweighed the helter-skelter performance of balloons. Low-altitude balloon experiments for propaganda leaflet drops or the transport of infantry soldiers remained in progress, but were transferred back to the 9th MTRI in Tokyo. The degree of importance given to this research is difficult to determine, although after the Doolittle Raid it was given higher priority. Balloon size was increased to six metres [19.6 feet] in diameter, which also increased its range. Two submarines, 1-34 and 1-35, had modifications made to their hatches to facilitate the launch of these new balloons off of the west coast of North America. This would never happen, as both subs were reassigned to the Guadalcanal operation. The new six-metre balloons had a range of about three thousand kilometres and could remain airborne for thirty hours at an altitude of 26,200 feet.3

When the Japanese Army took full control of the project it meant that launches would have to be made from the home islands. The balloon diameter was increased further to ten metres [32.8 feet], while instrumentation was developed to work at higher altitudes and bomb payloads were recalculated. The 5th Army Technical Research Institute developed a high-altitude battery and instrumentation that allowed test units to be tracked as far as 130 degrees west longitude. Project engineers were exuberant over the trial results and decided to go ahead with offensive operations, choosing the period of November 1944 to March 1945 for their launch envelope.

The Imperial Navy started a balloon programme that paralleled the Army's in 1942, using a rubberized silk fabric for their envelopes. Known as the "Internal Pressure Type," the production model had a gas-release valve that would vent hydrogen when it reached a pressure of 50mm Hg [by mercury barometer]. The valve system allowed this model to fly at a steady altitude. Brought into the Army programme as Balloon Type B, it was noted that the payload of the rubberized silk envelope was less than that of the paper balloons. Therefore, the Type B was employed to carry radio-tracking transmitters, one being launched with each group of bomb-carrying paper balloons. When it was decided that development had progressed to the point that the Balloon Offensive could begin, contracts were let out for the production of 10,000 balloons to be ready for the November-March period of 1944-1945.4

The production models which carried armaments were characterized by spherical 33-foot diameter paper envelopes. A rope-reinforced catenary curtain horizontally surrounded the envelope slightly below its midsection. Nineteen suspension lines 45 feet in length were attached to the catenary curtain. These lines were then loop-spliced through a steel load-ring which was slung vertically. Attached to the load ring were four double ropes that were eye-spliced through cap nuts on top of the gondola, or "chandelier." A rubber shock-cord was installed between the load-ring and a point where the double ropes attached to the chandelier forming a pyramid. The base of the envelope had a small appendix used to fill the balloon with hydrogen gas, and to carry the gas-relief valve. This valve was set to bleed excess pressure of expanded hydrogen when a force of approximately one-half ounce per square inch was exerted, a force well below the bursting strength of the paper.5


1. For an account of the Doolittle Raid, see Carroll V. Glines, The Doolittle Raid [New York: Orion Books, 1988].

2. Robert C. Mikesh, Japan's World War II Bomb Attacks on North America [Washington: Smithsonian Institute Press, 1973; Number 9 Smithsonian Annals of Flight]; Peter Williams and David Wallace, Unit 731 [Hodder and Stoughton, 1989].

3. Robert C. Mikesh, op. cit.

4. Ibid.

5. R.W. Mackay, “Japanese Paper Balloons”, The Engineering Journal, September 1945. McKay prepared this article for the Canadian Army Operational Research Group, Department of National Defence.

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