What are spy balloons and why are they still being used?

STORY: This video captures what is thought to be a Chinese "surveillance balloon" flying over the United States.

Using high-altitude balloons for spying and other military missions is a practice that dates to the middle of the last century.

Here is what is known about how they operate and what they can be used for.

During World War II, the Japanese military tried to loft incendiary bombs into U.S. territory

using balloons designed to float in jet stream air currents.

During the Cold War, the U.S. military started exploring the use of high-altitude spy balloons,

which led to a large-scale series of missions called Project Genetrix.

According to government documents, the project flew photographic balloons over Soviet bloc territory in the 1950s.

During the war in Afghanistan, spy blimps were central players in the U.S. military’s shift toward using technology for surveillance and intelligence.

Equipped with infrared and color video cameras and microphones, the blimps could stream video and audio in real time.

(Mohammad Lalai, Kandahar resident) "These security blimps must be removed from the sky, because it is monitoring our homes and invading our privacy."

And more recently in 2021, the EU’s border agency also used a surveillance balloon to detect migrants boats.

The blimp aimed to give border officials a clearer view of approaching boats.

So what are the advantages of using spy balloons over satellites?

They typically operate at 80,000 to 120,000 feet

well above where commercial air traffic flies.

The advantages of balloons over satellites include the ability to scan wide swathes of territory from closer in.

They're also able to spend more time over a target area, according to a 2009 report to the U.S. Air Force's Air Command and Staff College.

And, unlike satellites, which require space launchers that cost hundreds of millions of dollars, balloons can be launched cheaply.