Small explosive, chemical, or gas bomb used at short range. Invented in the 15th century, it became so important that 17th-century European armies had specially trained grenade throwers, or grenadiers. After c. 1750 grenades were largely abandoned because the increasing range and accuracy of firearms had lessened opportunities for close combat. They returned to widespread use in the 20th century, when their effectiveness in World War I trench warfare made them a standard part of the combat infantryman's equipment, which they have remained. Most common is the explosive grenade, with a core of TNT or another high explosive encased in an iron jacket and a fuse that detonates it either on impact or after a brief (usually four-second) delay. Chemical and gas grenades generally burn rather than explode.