TIL that Japan weaponized the airstream in WWII to send bombs into North America

Some other interesting tidbits, if you're not familiar with them.

Japan twice shelled locations in the contiguous US from the deck gun on submarines, though the shelling caused very limited damage.

https://en.wikipedia.org/wiki/Bombardment_of_Ellwood

Firing in the dark from a submarine buffeted by waves, it was inevitable that rounds would miss their target. One round passed over Wheeler's Inn, whose owner Laurence Wheeler promptly called the Santa Barbara County Sheriff's Office. A deputy sheriff assured him that warplanes were already on their way, but none arrived. The Japanese shells destroyed a derrick and a pump house, while the Ellwood Pier and a catwalk suffered minor damage.

https://en.wikipedia.org/wiki/Bombardment_of_Fort_Stevens

Most Japanese rounds landed in a nearby baseball field or a swamp, although one landed close to Battery Russell and another next to a concrete pillbox. One round damaged several large telephone cables, the only real damage that Tagami caused. A total of seventeen explosive shells were fired at the fort.[5]

Japan tried to firebomb the contiguous US to start forest fires from a floatplane that was carried, disassembled, in a large submarine.

The impact was also limited, though one did start a fire that was extinguished.

https://en.wikipedia.org/wiki/Lookout_Air_Raids

On September 9, 1942, a Japanese Yokosuka E14Y Glen floatplane, launched from a Japanese submarine, dropped two incendiary bombs with the intention of starting a forest fire.

Fujita dropped two bombs, one on Wheeler Ridge on Mount Emily in Oregon. The location of the other bomb is unknown. The Wheeler Ridge bomb started a small fire 16 km (9.9 mi) due east of Brookings.[6]

The two men proceeded to the location and were able to keep the fire under control.

Ultimately, the town and the pilot wound up ending things on pretty good terms:

Twenty years later, Fujita was invited back to Brookings. Before he made the trip the Japanese government was assured he would not be tried as a war criminal. In Brookings, Fujita served as Grand Marshal for the local Azalea Festival.[1] At the festival, Fujita presented his family's 400-year-old samurai sword to the city as a symbol of reconciliation. Fujita made a number of additional visits to Brookings, serving as an "informal ambassador of peace and friendship".[7] Impressed by his welcome in the United States, in 1985 Fujita invited three students from Brookings to Japan. During the visit of the Brookings-Harbor High School students to Japan, Fujita received a dedicatory letter from an aide of President Ronald Reagan "with admiration for your kindness and generosity". Fujita returned to Brookings in 1990, 1992, and 1995. In 1992 he planted a tree at the bomb site as a gesture of peace. In 1995, he moved the samurai sword from the Brookings City Hall into the new library's display case. He was made an honorary citizen of Brookings several days before his death on September 30, 1997, at the age of 85.[8] In October 1998, his daughter, Yoriko Asakura, buried some of Fujita's ashes at the bomb site.

Japan had used biological weapons in China and also considered use of biological weapons in the US, dropping bubonic plague.

This was not ultimately carried out. Had it been done, it would have happened very late in the war, with Japan being in pretty dire military straits at that point.

https://en.wikipedia.org/wiki/Operation_PX

Operation PX (Japanese: PX作戦, romanized: PX Sakusen), also known as Operation Cherry Blossoms at Night (夜桜作戦 Yozakura Sakusen)[1] was a planned Japanese military attack on civilians in the United States using biological weapons, devised during World War II. The proposal was for Imperial Japanese Navy submarines to launch seaplanes that would deliver weaponized bubonic plague, developed by Unit 731 of the Imperial Japanese Army, to the West Coast of the United States. The operation was abandoned shortly after its planning was finalized in March 1945 due to the strong opposition of General Yoshijirō Umezu, Chief of the Army General Staff.

The plan for the attack involved Seiran aircraft launched by submarine aircraft carriers upon the West Coast of the United States—specifically, the cities of San Diego, Los Angeles, and San Francisco. The planes would spread weaponized bubonic plague, cholera, typhus, dengue fever, and other pathogens in a biological terror attack upon the population. The submarine crews would infect themselves and run ashore in a suicide mission.[3][4][5][6]

I considered making a [email protected] post for this, but these were used for war, not fun. It sure was creative, so I'm tagging this as #balloons anyway.

Radiolab did an episode on this a few years back; it was prety good.
https://radiolab.org/podcast/war-our-shore-2305/transcript