From Mechwarrior Living Legends Wiki
The Laser Anti-Missile System, or LAMS, consists of one or more automated defense turrets that target and shoot down any enemy Missiles that fall into its range. Utilizing a rapid-fire Pulse Laser, it is capable of destroying an LRM in a single shot, but multiple shots are needed to destroy the much larger and more powerful ArrowIV.
It should be noted that visible laser beam from LAMS isn't where actual damage is delivered. LAMS has nearly 100% accuracy and instant aiming mechanics. It's unrelated to effect player can see. Reason for this were difficulties with proper aligning of the visual effect that were impossible to be fixed.
Bases are also protected by larger, stationary version of LAMS. These turrets feature much greater range than standard LAMS, but also they are able to shoot down incoming and outgoing Long Tom shells, Tbolts and Firebombs, unlike standard, mobile version of LAMS. These turrets shoot both friendly and enemy missiles, resulting in damage to units attempting LRM camping from base.
AMS was included in MWLL 0.2.0, through in 0.3.0 it was renamed to it's canon designation, the LAMS. Version 0.3.0 added also the LAMS Turrets.
Typical BattleTech AMS utlizes short-range, rapid-firing Ballistic Weapons; however, what is currently implemented in MWLL is the Laser Anti-Missile System, which uses a compact Pulse Laser - when firing, it could develop relatively large amounts of waste heat, forcing equipped Mechs and Vehicles to manage it well or install additional Heat Sinks. The advantage of LAMS was that it did not require ammunition, making them capable of defending the equipped unit during long battles.