- It doesn't have the space for it.The Atlas' missile tubes are all in its right torso - right next to the ECM on the D-DC. This means that you can have, at most, 35 missiles per salvo on that chassis, or 40 on the D or RS - unless you're deliberately gimping yourself by forgoing ECM and/or Artemis. This is an insufficient throw weight around which to build a 100-ton Battlemech.
- You're wasting tonnage on excessive ammunition. A "pure" Atlas missile boat with a 325 STD, 35ALRMs, TAG, and a Medium Laser (like Dave Barry, I swear I am not making this up) will have enough ammunition and heat sinks to sustain fire for seven minutes and 51 seconds. That means that if he had a target that whole time, he could pound out indiscriminate LRM fire for longer than the combat phase of many matches actually lasts. Of course, this is not realistic - realistically, you'll have periods where there's no targets, or choose not to engage an intermittent lock - but even if you're firing 75% of the time, you'll still have ammunition for a staggering nine minutes and 14 seconds of combat. This is simply too much ammo, even if you come to the battle foolishly intending to indiscriminately rain everything that moves.
- Or an overlarge engine. Atlas engines are expensive; at the upper range of ratings - say 325 and higher - the tonnage to increase your engine size ramps up heavily, for only a minor increase in overland speed. Higher engine ratings also affect your torso maneuverability and turn rate, however, so brawlers often pay the tonnage tax to mount fast engines - but an LRM boat with no real secondary guns does not benefit nearly so much from a big engine. For example the 6.5 ton difference between a 325 and 350 rated engine could be spent on weaponry rather than 4.5 kph - without sacrificing the builds LRM-centric goals.
- Every single alternative does it better. Seriously: every single one. No matter what Atlas chassis you choose (most choose the D-DC,) there is a Stalker that does it better; or a Highlander; or a Battlemaster; or an Awesome. Only the Victor and Banshee are outclassed by the Atlas as a missile platform - all the other chassis have at least one variant that has better hardpoints, tubes, and critical space.
- Your energy hardpoints are very low. The Atlas' energy hardpoints are at about waist-level. You're shooting from the hip, which means that you have to expose a very large portion of your silhouette to use TAG (even if you use a corner, you have a very broad 'mech; same thing applies.) Since TAG is a critical tool for you to be able to get good effects with your missiles, this is a serious drawback.
- It doesn't have the tubes for it. You've only got one 10-tube and two 6-tube hardpoints on your D-DC; the other Atlases have less. This is why your missiles come out in a messy stream - which makes them more vulnerable to AMS, gives your target more opportunity to spread damage and seek cover, and slows their rate of fire (your launchers don't start to recycle till the last missile is away.)
Atlas missile boats, unless they isolate themselves, are frequently among the last to die - but this is not a good thing. What it means is that the enemy has been killing targets whose ratio of firepower to toughness is much higher than an Atlas LRM boat: Consider an AC/40 Jaegermech, or an Ultra AC/5 Illya Muromets build. Either of those 'mechs are considerably easier to kill, and bring much more direct firepower (i.e. they will kill you faster than an LRM boat.) So by removing your Atlas from the front lines, you've removed the option for the enemy to shoot at you, the hard target, rather than your glass cannon supports.
It's not my purpose in this post to insist that no one should never put any LRMs on an Atlas as part of a larger build. But boating LRMs through that chassis is simply a Bad Idea for empirical reasons. You may point out that you get high damage numbers with your Atlas LRM boat, but you'd get better numbers and performance from the superior alternatives I mentioned - and your team would be better off.
Finally, there are two things involved with any guide: First, all players have their own areas of aptitude as well as a general level of skill. If you're good enough with your specialty to maintain a positive win/loss ratio (KDR and damage are deceptive with LRMs and are not good measures of overall success) to excel in whatever build, don't stop because you read something on the internet - if it's working, treat countervailing guides as food for thought.
The second point to remember about any guide is that you're not allowed to be personally affronted by it. Any guide you read represents the writer's best analysis on the subject of the guide, and while you can object to his reasoning, or to actual rudeness, you don't have the right to be offended or hurt because someone disagrees with you on the internet.
This guide is my best analysis on what is wrong with boating LRMs on an Atlas: that the game's mechanics empirically disadvantage such builds, and that any pure-boat Atlas can be improved with the addition of significant secondary weaponry.
Edit,05MAY14: reformatted and added a point.
17MAY14: Revised now for great justice!
Edited by Void Angel, 19 May 2014 - 07:47 PM.