It is a prerequisite of space flight.
Although experiments with Rocketry trace back to Chinese fireworks powered by Gunpowder one thousand years ago, most of our current knowledge was developed in the 20th Century. A Rocket is propelled by the ejection of gases created by the Combustion of on-board fuel. The Combustion creates great pressure that is vented through the rear, and this thrust against the front interior of the Combustion chamber pushes the Rocket forward. The first practical guided Rockets were used in World War II. More recently, Rockets have been used to propel intercontinental ballistic weapons and launch spacecraft.