Two decades after World War II, American forces entered into the Vietnam Conflict and required a new weapon to face a new enemy on a new battlefield. The heavy hitting (and flat-out heavy) M14 was developed and deployed but short-lived as a main battle rifle as its limitations were exposed in the conflict. It was replaced by the lightweight M16, a smaller-caliber .223 rifle described as a "Mattel toy" upon its initial deployment. It, too, was limited in battle, at first, lacking a chrome-lined barrel and chamber and cleaning instructions and equipment for operators. But with the introduction of the A1 model, the weapon began to prove its worth. Examined later in episode seven is the development of the A2 version and on through to today's M4 carbine. Also highlighted are the M60 machine gun, the M249 machine gun, the M79 "thumper" grenade launcher, and the M203 weapons-mounted grenade launcher. Of course, the piece also explores the origins and the proliferation of the AK-47.

Episode six begins with the development of the Thompson .45 caliber submachine gun and its wide usage in prohibition and depression era America in the lead-up to World War II. The evolution of the BAR into a fully automatic-only weapon, the development of the M1919, and the introduction of the venerable .50 caliber M2 or "ma deuce" machine gun, which even served as a sniper rifle in Vietnam by Carlos Hatchcock, are examined. The development and wartime usage of the classic M1 Garand, the first semi-automatic rifle to serve as standard issue for any army in the world, swallows much of this episode's runtime. Also featured are a plethora of small arms used in the European and Pacific theaters, including lighter automatic rifles such as the .30 caliber M1 carbine; the updated M1A1 carbine with a folding stock designed for use by paratroopers; and the stamped M3 submachine gun, better known as the "grease gun.

Episode five focuses largely on the U.S. weapons of World War I, a war in which American soldiers would first face the devastating Maxim machine gun, a weapon that used recoil to eject the spent casing and load the next round. Other machine guns highlighted are the crew-served German MG08, the .303 British Vickers gun, the Lewis gun with a 47-round drum magazine, the gas-operated Hotchkiss machine gun, and the Chauchat. Episode five also looks at the machine guns produced by John Moses Browning, including the M1917 and the Browning Automatic Rifle (BAR). Infiantry weapons highlighted include the American 1903 Springfield and P-14 (or American Enfield), the M1897 Winchester shotgun, the German G98, the British Lee-Enfield, and the French Lebel 1886 and Berthier models.

The 1873 "trapdoor" Springfield is the first focus of episode four. Also noted early is the Gatling gun that, by 1893, was capable of firing some 800 rounds per minute, spurring an advance in ammunition towards the development of the centerfire cartridge and the push towards the modern wave of firearms. Episode four examines the pioneering work of Smith & Wesson in the development of revolvers with rear loading cylinders, including the famed Models One and Three, the latter of which saw large sales to the Russian army. Meanwhile, Colt produced its Single Action Army 1873, or "Peacemaker," revolver. It was dubbed "the gun that won the West" along with the Winchester 1873 repeating rifle, both chambered in .44 caliber ammunition that was interchangeable between the weapons. Also highlighted is the emergence of other manufacturers such as Remington and Marlin and the introduction of smaller Derringers.

Episode three focuses in on the guns of the North and South, notably the smoothbore muskets on both sides, some converted to percussion guns, some not, and some coming straight from the armories as percussion tools. The episode looks at the evolution of arms in the Civil War, beginning with the model 1855, a smaller caliber but more accurate "tape primer" firearm invented by a dentist named Edward Maynard that ultimately proved unreliable in practice. The model 1861 was developed in response, a classic percussion fired weapon that added in a rear sight and that would become the most widely used arm in the war. Episode three also examines the Confederate raid on the Harper's Ferry armory and the Confederacy's dire need for arms and their purchase and trading of cotton for arms with Europe, notably acquiring the British Enfield and Austrian Lorenz.

The strain between the colonists and the British Parliament, the threat of conflict, and the colonists' stockpiling of arms and ammunition for use in the coming war for independence begins episode two. The segment examines the arms of both the colonists and the English, most of which were covered in the previous episode. Also featured are the weapons acquired form the French and those produced in the colonies. Episode two also looks at the flintlock handguns carried at the time of the revolution and General Washington's "buck and ball" loading system. Examined in detail is the battle of Lexington, the burning of supplies at Concord, and the Battle of Saratoga and the critical role of "Morgan's riflemen.. Episode two also sees the development of the Minié ball, which facilitated firing accurately from a rifled barrel, and the development of Sharp's rifle and its place in the pre-Civil War era. Also: the innovations of Samuel Colt in the development of handguns.

Episode one begins with the development of gunpowder by a Chinese alchemist, used for fireworks displays and later military applications, including gunpowder-packed arrows, cannons, and grenades. The episode examines the "fire lance," believed to be the first firearm. It was a bamboo tube with gunpowder and a projectile packed into it, highly effective but only at short ranges. Gunpowder remained a Chinese secret until the 13th century when Roger Bacon, a Franciscan monk, learned of it, saying, "the sound of thunder may be artificially produced in the air with greater resulting horror than if it had been produced by natural causes." As the episode jumps ahead to more modern times, it examines the development of hand cannons made of bronze metal tubes and the development of the Matchlock, the Wheellock, and the Snaplock..