First introduced in 2295 by the Terran Hegemony and refined in 2300, Long-Range Missiles are designed to engage the enemy at great distances at the expense of damage dealt. Adapted towards the profusion of electronic jamming on the battlefield and the effectiveness of standard armor designs, these self-guided missiles are unique for using a special armor-piercing explosive warhead. The development of a metal composite/high explosive mixture allowed for the warhead to be made entirely of high-explosive material; this same feature was later used to construct the missile's frame as well. The result were warheads which had the same destructive capability as older warheads that were four times as long, allowing for more missiles to be carried and fired. LRMs are capable of indirect fire and disperse over a smaller area than Short Range Missiles while causing less individual damage. Inner Sphere LRM launchers achieve their superior range by firing at a ballistic launch angle, making them less accurate at close range. Clan LRM launchers do not suffer from this effect, in addition to being smaller and more compact, thanks to their technological advantage. LRMs are highly upgradable, able to fire a variety of warheads and benefit from devices such as Artemis IV FCS.
Prototype LRM units, built between 2295 and 2300, have trouble with target acquisition, and as a result tend to hit a target less often in a given salvo. They also can only carry three quarters the ammo usually allocated, versus standard systems, per ton of ammo loaded.
Long-Range Missile technology has been expanded upon since it was first introduced, especially in the years since the Clan Invasion spurred weapons designers on both sides. These include Extended, Enhanced, and Streak LRMs, as well as scaled-down battle armor versions.
Nearly all LRM types (and ATM types, according to errata) can be "hot loaded", implying that their warheads and guidance systems are armed, even as they sit in the ammo stores of the vehicle. This effectively eliminates the minimum range issue that Inner Sphere LRM missiles have, but at a cost of accuracy.
Hot Loading LRMs
For tabletop play, minimum range modifiers are ignored for hot loaded missiles. When determining the number of missiles that hit, roll 3D6 dice and use the lowest two results for the cluster hit table. Ammo hot loaded this way is armed in the tube, and the launcher will explode if critically hit for the full damage value (i.e. 10 damage for an LRM-10), and may cause a randomly determined ammunition bin explosion in the same 'Mech location as the launcher on a separate 2d6 roll of 5 or less conducted when the launcher is hit. This separate roll is not made for vehicles since they store their ammo in the Body. Hot loaded ammunition must be assigned in full ton lots, and the ammo bins containing hot loaded missiles must be declared at the beginning of the scenario except for vehicles with a crew count more than 1 which, because they have onboard crews, may make the declaration during the End Phase and may switch back and forth in this manner. Equipment that modifies the cluster roll such as Artemis IV, TAG, and Narc still works with hot loaded missiles and adds its modifier as normal. 
- Interstellar Operations, p. 118, "Prototype Dates For Basic Weapons Table"
- TechManual, p.229
- Era Report: 2750, p. 99-100
- Interstellar Operations, p. 118, "Primitive Prototype Equipment
- Tactical Operations, p. 103, "Missiles"