Japanese Jellyfish Bomb

By: Alison

It’s a bird! It’s a plane! No, it’s a… bomb? In the 1940s, the Japanese developed a new type of bomb: the Japanese balloon bomb, more commonly known as the jellyfish bomb.

Keep reading to learn more about this unique war tactic and its uses.

The creation of the jellyfish bomb

All’s fair in love and war. When Japan went to war with the United States after the attack on Pearl Harbor, they started thinking of unpredictable ways to attack the U.S. from across the Pacific. They knew the Pacific Northwest region of the country had a great deal of trees and forestry, so they devised a plot to try and set fire to those forests.

To do so, Japanese scientists began a project called Fu-Go. They discovered a unique way to use the sweeping air stream that blows across the Pacific Ocean from Japan to the U.S. mainland and planned to send these jellyfish bombs to set fires, therefore dampening civilian spirit and causing chaos.

jellyfish bomb balloon

A jellyfish bomb looked similar to a hot air balloon. They measured roughly 33 feet in diameter, and they were capable of carrying at least 1,000 pounds. On each jellyfish bomb, the Japanese attached a 33-pound anti-personnel fragmentation bomb along with a 64-foot fuse. Once lit, the fuse would burn for about 80 minutes before finally detonating.

Without sacrificing a plane or a soldier, the bombs would silently attack the U.S. where they were least expecting it. It was said that when these balloons were launched together, they looked like schools of jellyfish. American scientists estimated that the Japanese launched about 6,000 of these bombs.

The effects of the jellyfish bomb

U.S. civilians didn’t report any sightings of jellyfish bombs until late 1944. Coal miners spotted the first one near Thompson, Wyoming. Just a few days later, another one was seen in Kalispell, Montana. Local law enforcement officials gathered the parts that remained after detonation and sent them to Butte, Montana, where military and FBI personnel examined them. They were able to determine that the jellyfish bomb had come from the Japanese, but they had no idea how.

jellyfish bomb Map

Once they figured out the Japanese plan, the U.S. military asked local news stations not to report the sightings and detonations of the bombs. We may never know exactly how many landed on U.S. soil or the extent the damage during the war.

There was one report during the war of a pregnant woman and five children killed by a jellyfish bomb on Gearhart Mountain in Bly, Oregon. For several years after the war, other reports began flowing in from cities in Nebraska, Michigan, California, Oregon and even Canada. By that time, it was permitted to report on the bombs.


During World War II, the Japanese sent hundreds of these jellyfish bombs towards the United States. Most of them have yet to be accounted for, but people are still finding them.

In October 2014, a group of forestry workers found a jellyfish bomb while working in Lumby, British Columbia – just 250 miles north of the U.S. border. Henry Proce, of the Royal Canadian Mounted Police, said the bomb was “far too dangerous to move,” according to an NPR report. In the end, it was safely destroyed.

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