Rocketry

While the rocket was first invented and used by the Chinese over three thousand years ago—and used occasionally by the Greeks and Romans since —it wasn’t until the twentieth century that it came into its own and became more than just a dazzling amusement or a largely harmless but still effective “terror weapon” for ancient armies. In the twentieth century, rockets became bigger and more powerful. Most importantly, they became controllable, which suddenly made them useful both as weapons of war and, even more vitally, as our means of accessing outer space. Without the rocket, it is safe to say we would not only have never gone to the moon or visited every planet in our solar system. Rockets also place satellites into orbit around our planet, so without them we also wouldn’t be able to use GPS, predict the weather, make international calls or, for the most part, even use our cell phones much of the time.
Source:http://www.toptenz.net/top-10-inventions-of-the-20th-century.php