An F-22 downed a Chinese spy balloon on Saturday with a single AIM-9X Sidewinder missile.
But the Pentagon wasn't sure if the missile would work when the pilot fired it, a top commander said.
The debris from the balloon plummeted over 60,000 feet into waters off the coast of South Carolina.
A US Air Force F-22 fighter jet fired a single air-to-air missile at a Chinese surveillance balloon over the weekend, sending the system crashing into the Atlantic Ocean in a moment of heightened tension between Washington and Beijing.
But before the pilot took the shot on Saturday, the US military wasn't sure that the missile would actually work for this specific operation, a top US commander said on Monday.
The F-22, which was operating at an altitude of 58,000 feet, used an AIM-9X Sidewinder air-to-air missile to take down the balloon, which was hovering between 60,000 and 65,000 feet, a senior US defense official told reporters after the mission.
Gen. Glen VanHerck, commander of NORAD and US Northern Command, told reporters on Monday that he was unsure if the Air Force ever tested an AIM-9 against a balloon target at such a high altitude.
"I'm not aware of any engagements against the high-altitude balloon such as this. We did not have the weapons data," he said.
VanHerck was asked in a follow-up question why the US decided to use the short-range AIM-9 missile instead of the advanced medium-range AIM-120 - a beyond-visual-range missile that can operate in all weather conditions.
VanHerck said the AIM-120 has a "significantly" longer range and a bigger warhead, making it less safe than the AIM-9. "We assessed from an effectiveness standpoint that it was going to be highly effective, and that was proven on Saturday," VanHerck said of the AIM-9.
Weapons evaluators for the Air Force could not immediately address Insider's inquiry on the matter.
The AIM-9 Sidewinder is a supersonic heat-seeking missile, the first of which was developed by the US Navy in the 1950s and adopted by the US Air Force years later. It is powered by a rocket motor, carries a high-explosive warhead, and uses infrared guidance to home in on an aircraft's engine exhaust.
The AIM-120, on the other hand, is a "new generation" missile that succeeded the AIM-7 Sparrow, according to the Air Force. At nearly 12 feet long, it's significantly longer than the AIM-9 and has a heavier launch weight of 335 pounds compared to 190 pounds for the AIM-9.
China's spy balloon was downed by the newest variant of the AIM-9, the AIM-9X, which has smaller fins than previous versions. Not only was this apparently the AIM-9s first high-altitude balloon target, but this was also the first air-to-air kill by the stealthy fifth-generation F-22 Raptor, which used the callsign "FRANK" in a nod to a legendary aviator who downed over a dozen German military balloons during World War I.
The debris from the balloon fell into waters roughly 47 feet deep off the coast of South Carolina, a senior US military official said on Saturday. VanHerck said on Monday that US forces have begun the process of recovering the debris, which fell in an area as large as "15 football fields by 15 football fields." The Navy released the first photos of the balloon recovery operation on Tuesday.