China has tested a weapon that was previously thought impossible, according to a new report.

The hypersonic weapon test saw the country fire a missile from another spacecraft that was already flying at least five times the speed of sound, the report claimed. Such technology was previously thought impossible and US experts are unsure how China was able to actually conduct the test, it said.

Though the test happened in July, and was reported closer to the time, the nature of the breakthrough was first revealed in a new report from the Financial Times. The paper reported that experts have been poring through data in an attempt to understand how China was able to build the technology – as well as what exactly the missile was intended to do.