During World War II, the Japanese used the air current across the Pacific ocean to send bombs attached to hydrogen balloons to the United States. This was known as the Fu-Go campaign.
Balloons could reach the United States in as little as 30-60 hours depending on weather conditions. It is estimated the Japanese sent approximately 9,000 balloons our way, but only 342 were confirmed to have reached the United States.
In 1944, a balloon landed and exploded killing an entire family in 1944. There could be many balloons that reached that reached the United States and did not explode, but they have not been found.