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 10 m (33 ft) in diameter and, when fully inflated, held about 540 m3 (19,000 cu ft) 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.
Read more about this topic: Fire Balloon