When a weather balloon went rogue almost 25 years ago, fighter jets fired 1,000 rounds at it and couldn't bring it down

• About 25 years ago, a rogue weather balloon wouldn't come down after over 1,000 rounds were fired at it.
• The balloon entered Icelandic air space and drifted north towards Norway. 
• Balloons, like the Chinese "spy balloon" over the US, don't always pop or explode when shot. 

Almost 25 years ago, a large runaway weather balloon proved to be quite challenging for a pair of fighter jets trying to shoot it down, staying in the air even after more than 1,000 rounds were fired at it.

The research balloon was measuring ozone levels above Canada, the Associated Press reported at the time. It went rogue in August 1998, passing across Canada, over the Atlantic Ocean, and through British airspace before entering Iceland's airspace and then drifting north. 

Two Royal Canadian Air Force CF-18 fighter aircraft spotted the balloon over Newfoundland and fired more than 1,000 rounds at it. The AP reported that the jets, Canadian variants of the American F/A-18 Hornet, hit the balloon, but rather than popping or exploding and crashing to the earth, it slowly began leaking helium. The big balloon was still in the air.

A Canadian military spokesperson, a lieutenant named Steve Wills, told BBC that it was difficult to target the balloon, even though it was about the size of a 25-story building, and that the failure to take it out wasn't embarrassing.

"With something like this, which is stationary in the air when the CF-18s are flying very, very fast, it is difficult to shoot it," Wills said.

The CF-18s were reportedly equipped with air-to-air missiles, but Canadian Major Roland Lavoie told AP the pilots refrained from using them. 

"Citizens would not have appreciated having a missile blowing over their heads,″ he said. "Also, it might be overkill spending a couple of hundred thousand dollars on a missile to shoot down a balloon that's drifting away."

The balloon also survived encounters with British and American aircraft.

According to reports from the time of the incident, the 300-ft helium balloon prompted air traffic controllers to divert and delay transatlantic flights. If deflated, the balloon would cover an area of about five football fields, The Irish Times said.

Earlier this year, a Chinese spy balloon passed over the US and was shot down by the military, prompting widespread security concerns.

After being collected by US Coast Guard officials, the balloon's wreckage was found to include American-made technology that helped it gather photos, videos, and other information for China. 

News of the balloon including US tech were first reported last week by The Wall Street Journal, while NBC News said the Biden administration believed the aircraft featured American materials shortly after it was detected back in February. 

Officials told the WSJ that while the balloon collected surveillance data, there was no apparent or immediate transmission of that information back to Beijing. 

But last Thursday, the Pentagon contested that the balloon had even collected information during its flight, with Brig. Gen. Patrick Ryder telling CNN: "We believe that [the balloon] did not collect while it was transiting the United States or flying over the United States, and certainly the efforts that we made contributed."