4
Except for Narc (covered at the end of this post), Missile weapons are characterized by the maximum number of projectiles they fire (salvo size) with each trigger press. An LRM 20 may fire up to 20 missiles at a time, while an SRM 6 may only fire up to 6. Each projectile does a certain amount of damage if it hits the target.
All Missile weapons require ammunition which is is stored in critical slots on the mech. Ammo is installed in single slot increments. There are specific types of ammo for LRMs, SSRMs, and SRMs but these can be shared by different launcher sizes of the same type. For example, a mech with one SRM6, an SRM4 and an SRM2 would only need generic SRM ammo. If a SSRM2 launcher were added, SSRM ammo would be required. Generally, ammo is bought in one ton lots, but it is possible to buy 1/2 ton lots which take one slot but weigh less. Ammo location on the mech does not matter, e.g., ammo stored in the left leg will be magically fed to a weapon in the right arm without delay.
While each weapon has a maximum salvo size, it is important to note that Missile hardpoints have a restriction not found on Energy and Ballistic hardpoints: tubes. Each Missile hardpoint on a mech is assigned a number of tubes. This information is not available in the game’s mechlab--it must be looked up on 3rd party sites such as Smurfy. Each Missile hardpoint may only fire as many projectiles at a time at there are tubes on on that hardpoint. For example, the Thunderbolt 9S has one left torso Missile hardpoint with 10 tubes. If an LRM 5 or LRM 10 were installed, they would be able to fire their entire maximum salvo size at once. However, an LRM 15 would fire 10 projectiles and then 5 more in two salvoes. An LRM 20 would fire two salvoes of ten and ten.
In addition to tubes, some Missile hardpoints have an additional unique feature: bay doors. Again, 3rd party sites are your reference for mechs with this feature. A Missile hardpoint with a bay door has a panel covering the launcher. When the player presses the trigger, this panel must open to fire the salvo, causing a short delay. While closed, the panel provides a small bonus to the durability of that section of the mech. There is a keybinding to open the bay doors on a mech and a cockpit indicator of the current bay door status, Amber is closed, green is open.
Missile weapons can be categorized as either lock-on/seeking or dumb fire. LRMs and SSRMs are lock-on/seeking, SRMs (and Narc) are dumb fire.
The lock-on mechanic works like this. The target must be in sensor range of your mech or targeted by a team member’s mech (or Narc'd). This is indicated by a unfilled red downward-pointing triangle over the enemy mech. The mech must then be targeted using the Target Lock key. At this point the enemy mech will be bracketed in a red box. If your mech has weapons using the lock-on mechanic, pointing your targeting reticle at the targeted mech will begin the lock-on process. The visual indicator for this is a spinning white circle. When this circle becomes red you may fire the seeking weapon. Moving the reticle away from the target for more than about a second will break the lock, and if the target breaks line of sight with all mechs on your team the lock is lost after a brief period (called target decay).
While a target is being tracked by locked-on missiles an icon appears next to the target’s location indicator (Dorito) for all players. The player being attacked also receives an incoming missile warning.
LRMs
LRMs (Long Range Missiles) generally use the lock mechanic and are a seeking weapon. LRM projectiles travel in an arc, allowing them to be fired over intervening cover. It is common for one mech to act as a ‘spotter’, allowing LRM-equipped mechs to fire on enemies to which they do not have line-of-sight. LRMs also have a minimum effective range. For Inner Sphere (IS) mechs, LRMs do no damage to targets closer than 180 meters. Clan LRMs can do small amounts of damage within the minimum range--this damage is negligible below 90m and rapidly increases as you approach 180m.
LRMs will track a moving target as long as the firing mech has a lock. If the lock is lost, the LRMs will strike the point where the target was at the time the lock was lost. It is possible to reacquire lock while the LRMs are in flight--if this is done early enough the LRMs will redirect to the target’s new location.
LRMs may be dumb fired (that is, without a lock). When LRMs are dumb fired they travel to the point under the reticle and strike the ground there, possibly causing damage to mechs in the area.
As each LRM salvo is spread over a small area, the damage a particular LRM salvo causes is spread over the target and some projectiles may miss. The larger the salvo size, the greater the spread. It is possible for very fast mechs to avoid a large number of projectiles in a salvo.
A note on Clan versus IS LRMs: Consistent with the damage-over-time nature of Clan weapons, Clan LRMs do not fire in distinct salvoes like IS LRMs. Clan LRMs ripple fire, that is, they launch as a continuous stream of projectiles until the salvo size is reached. This has the effect of the salvo reaching the target two or three projectiles at a time in rapid succession.
SSRMs (Streaks)
SSRMs (Streak Short Range Missiles, or Streaks) are the second lock-on/seeking Missile weapon. Unlike LRMs, Streaks must have a lock on to fire. Also, they do not have a minimum range. Streaks travel in a horizontal seeking path to the target (that is, they do not arc vertically like LRMs). Generally, all Streaks in a salvo will strike the target and the hit location of each Streak projectile is determined randomly. Streak projectiles do more damage than LRMs, but less than SRMs.
SRMs
SRMs (Short Range Missiles) are dumb-fire weapons--they do not require a lock. SRMs do not have a minimum range. When an SRM is fired, the projectiles spread out in a cone until they reach a certain distance from the firing mech--at that point they travel in a straight line until hitting something or self-destructing. SRM projectiles do more damage than LRMs or SSRMs.
Narc Beacon
Narc Beacons are the final type of item which can be fitted to a Missile hardpoint, though unlike the other types, Narc is a not a weapon itself but a support mechanism for other Missile weapons. When a Narc launcher is triggered, a single slow moving projectile is fired at the target. Narc does not require a lock to use, and like SRMs travels in a straight line to its maximum range. If the Narc projectile strikes an enemy mech, all friendly mechs will receive a bonus to targeting and missile strikes against the Narc’d target. This effect lasts a brief time (currently 30 seconds) and is indicated to all players by an icon next to the HUD's location icon (Dorito). The player who is NARC'd will see an orange "NARC" icon displayed slightly above the throttle indicator on the HUD.
You cannot Narc a friendly target. The Narc beacon itself does no damage.
Narc’ing a target improves the missile lock on the affected mech. This means that incoming guided projectiles will strike in a tighter pattern (75% of normal) potentially doing more damage to the target. It decreases the time required to establish a lock by mechs which do not have line-of-sight to the target. It also extends the target decay, the time lock is maintained when a target breaks line-of-sight.
Narc is also able to disrupt ECM--if a mech carrying ECM is struck by a Narc beacon that mech’s ECM is disabled for the duration of the Narc effect.
There used to be a mechanic where damage to a Narc’d mech had a chance to destroy the Narc. This is no longer the case.
Artemis IV Fire Control System
Artemis is a Missile-related upgrade found in the mechlab upgrades menu. Adding Artemis to a mech changes all LRMs and SRMs on the mech to a new type (LRM + Artemis and SRM + Artemis). Artemis has no effect on SSRMs. [Or, at least, it shouldn't. I belive there is a low priority bug that reduces SSRM lock-on time when Artemis is installed.]
Artemis Missile systems weigh one more ton and require one more critical slot to fit. They also require Artemis ammo--this should be the only ammo type presented if Artemis is installed. Artemis ammo weighs the same as non-Artemis.
Artemis provides a benefit to the firing mech similar to the effects of a Narc’d target. Artemis projectiles are more tightly clustered and so deliver more damage to the target (this affects SRMs as well). The spread of Artemis Missile weapons is 75% that of normal. Targeting time and target decay are reduced [need to verify this
]. However, the Artemis effect is only included when the mech with Artemis has line-of-sight with the target themselves. Indirect fire using a team member’s line-of-sight does not benefit from Artemis.How Artemis, Narc, and TAG interact
Artemis, Narc, and TAG (described fully in the Energy article) all provide benefits that relate to targeting and the use of Missile weapons. These three systems interact in the follow ways:
- Artemis and TAG effects stack. Artemis and Narc do not stack.
- TAG and Artemis effects stack. TAG and Narc effects stack.
- Narc and TAG effects stack. Narc and Artemis do not stack.
MWO calculates stacked negative bonuses by multiplying the percentage effects and applying the result. If three bonuses affect the same thing, and one provides a -40% effect, the second a -20% effect, the last a -10% effect, the total effect is a -56.8% reduction.
The math works like this. A -40% bonus reduces the thing to 60%, a -20% bonus reduces it to 80%, and a -10% bonus reduces it to 90%. 60% * 80% * 90% = 43.2%. Subtracting this from 100% gives the combined effect (100% - 43.2% = 56.8%).
Positive bonuses are added then applied. A +40%, +20% and +10% set of bonuses result in a +70% effect.
So, for Artemis, Narc and TAG:
Artemis + TAG:
- Time to lock onto target: (50% + 50%): 25% of normal
- Missile spread: (67% + 75%): 50.3% of normal
- Time to lock onto target: (50% + 75%): 62.5% of normal
- Missile spread: (75% + 75%): 56.3% of normal
Other Information
As with other weapons, there are modules which affect Missile weapon performance. There is also equipment that affect Missiles: AMS, ECM, BAP, Command Console, and Targeting Computer are covered in my article on Equipment. TAG is covered in the article on Energy weapons.
This is one of a series of articles on concepts in MWO. If you found this article helpful, you may wish to read the other articles listed in this post.
Edited by Gauvan, 31 August 2015 - 03:16 PM.
to the point were I have a 
