20th century assault rifles became a revolutionary weapon combining firepower, compactness and versatility, making them the main infantry weapon. The first mass-produced machine gun was the German StG 44, developed in World War II and using an intermediate cartridge, which combined the accuracy of a rifle and the rate of fire of a submachine gun. The Soviet AK-47, created by Mikhail Kalashnikov, became the most famous and widespread machine gun in the world due to its reliability, simplicity and efficiency. In the 1960s, the American army adopted the M16 assault rifle, which was distinguished by its lightness, high accuracy and the use of small-caliber cartridges. Machine guns of the 20th century were actively used in most conflicts, from the Vietnam War to the Afghan War, becoming a symbol of modern warfare. At the end of the century, models such as the Israeli Tavor and the Belgian FN F2000 appeared, which used the bullpup layout to increase compactness without losing barrel length. Automatic rifles began to be equipped with Picatinny rails for mounting optical sights, laser designators, tactical flashlights and other accessories. They have also adapted for use in a variety of environments, including urban combat, jungles, and deserts. By the end of the 20th century, automatic rifles had become modular, allowing them to quickly change barrels, butts, and other components for various tasks.