This episode unravels the history of the deadly rapid-fire weaponry favoured by both military and gangsters. We examine how 150 years of machine gun evolution has placed the firepower of a 19th Century Army in the hands of a company of US Marines. Specially staged live-fire machine gun events explain the key moments in the weapon's history: from the World War I machine gun that can chop down a tree, to the first gangster "hit" with a Tommy Gun, to the modern GAU-8 Avenger - one of the deadliest machine guns in the world.