Multiple rocket launcher

A multiple rocket launcher (MRL) or multiple launch rocket system (MLRS) is a type of rocket artillery system. Rockets have different capabilities than artillery, like longer range, and different payloads, typically considerably larger warheads than a similarly sized artillery platform, or multiple warheads. Unguided rocket artillery is notoriously inaccurate and slow to reload, compared to artillery. To overcome this, rockets are combined in systems that can launch multiple rockets simultaneously. Modern rockets can use GPS or inertial guidance, to combine the advantages of rockets with high accuracy.

The first multiple rocket launchers were made in Song-dynasty China. It was a primitive design where multiple fire arrows were fired from a gunpowder box. These also appeared later, in an expanded version, in the Joseon Dynasty of Korea, where they were used with great effectiveness against the Japanese Invasions of 1592-98, most notably the Battle of Haengju.

The first self-propelled multiple rocket launchers — and arguably the most famous — were the Soviet BM-13 Katyusha, first used during World War II and exported to Soviet allies afterwards. They were simple systems in which a rack of launch rails was mounted on the back of a truck. This set the template for modern multiple rocket launchers. The Americans mounted tubular launchers atop M4 Sherman tanks to create the T34 Calliope rocket launching tank, only used in small numbers, as their closest equivalent to the Katyusha. The Germans began using a towed six-tube multiple rocket launcher during World War II, the Nebelwerfer, also called the "Screaming Mimi" by the Allies.

Simple MRL types still have a reputation of having a devastating morale effect on ill-disciplined or already shaken troops. The material effect depends on circumstances, as well-covered field fortification provide much protection.

MRL are still rarely able to properly shoot at rear slope positions in mountain warfare because the MRL crew cannot determine the trajectory as well as a howitzer's crew can do by adding or removing propellant increments. Simple MRL rocket types have a rather long minimum firing range for the same reason. An approach to lessen this limit is the addition of drag rings to the rocket nose. The increased drag slows the rocket down relative to a clean configuration and creates a less flat trajectory. Pre-packaged MRL munitions such as with MLRS do not offer this option, but some MRL types with individually-loaded rockets do.

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