Ever since the invention of the grenade
way back when, users of said grenades (typically soldier
s) have wanted to be able to project said grenades farther
. Initially, this was mostly to ensure their own safety from the dangerously unpredictable things; later, as fuzing
mechanisms began to become safer and more reliable, the distance was desirable in order to be able to use them while as far from the enemy as possible.
The first standardized (i.e. not one-off hand-built) mechanisms for firing grenades - i.e. "grenade launchers" - were rifle grenade systems. The Russian army had a large number of early experimental rifle grenade systems in the latter part of the nineteenth century, but the concept still hadn't been perfected by the time World War I rolled around.
Early rifle grenade launchers were either specially built grenades or (more frequently) cup-shaped launchers which attached to the end of the rifle barrel. In some simpler (but more dangerous) versions, either the user would need to specially load a blank round or the grenades had a 'bullet catcher' built into their rear ends, and the user simply fired a normal rifle round into the grenade launcher. The force from the bullet would toss the grenade forward.
This, however, besides being prone to creating bullet fragments and not being as controllable as soldiers would like, forced the grenades to spend more of their weight and substance on structures designed to catch the bullet and not on the bits intended to kill the enemy, reducing their effectiveness. World War I ended up being fought with awkward hand grenades, improving as the war went on, and with not-terribly-effective rifle grenades.
During the interwar period, the U.S. fielded the M7 rifle grenade launcher as an attachment to the M1 Garand semiautomatic rifle. These took advantage of the fact that the Garand was gas-operated; attaching to the bayonet mounting system (lugs), the M7 was also attached to a valve allowing the operating gas from the rifle into the launcher. This gas charge entered the chamber and propelled the grenade forward. Later versions had propellant charges on the back of the grenade which were ignited by the rifle gas, propelling them farther.
At this point, rifle grenades and grenade launchers began to split apart, with rifle grenades becoming disposable accessories to the rifle and grenade launchers moving towards being reusable, dedicated components.
One of the first dedicated grenade launchers was the U.S. M79, fielded in time for the Vietnam War. Known as a 'bloop gun' for the noise it made, the M79 looks like a large, slightly misshapen shotgun. It is single shot and breechloading, breaking at the base of its 40mm barrel, and fires purpose-made grenade cartridges which look like large, fat bullets. This weapon is effective from point-blank (using 'beehive' or flechette rounds for direct fire) out to approximately 300 meters, where mortar fire becomes available.
In addition to the M79, the U.S. fielded the M203, which was an attachment to the Colt M16 assault rifle. Essentially a short 40mm barrel, it is attached under the front barrel of the M16 and has a separate trigger. Single-shot like the M79, it can be used to fire 40mm grenades out to ranges of 200 meters or so accurately.
As the 1980s rolled around and the prospect of massive armored formation combat began to occupy everybody's minds in Central Europe, the automatic grenade launcher such as the American Mk. 19 came into vogue as a popular accessory mount on Infantry Fighting Vehicles such as the Russian BTR-90 and the American Stryker. Belt-fed, these large automatic weapons can fire several DPICM grenades a second out to distances of over 1,500 meters, and are highly effective against both infantry and light vehicles. The Mk. 19's DPICM 40mm grenades can penetrate up to two inches of RHA armor, if they hit it properly (at zero angle).