"I do not fear an army of lions, if they are led by a lamb.
I do fear an army of sheep, if they are led by a lion."
All these things to think about while playing, but first, don't we need an army?? Perhaps this is a bit out of order, but I think I wanted to introduce some other concepts before I got to this because we're going to use them to make decisions about what to include in the army.
First, you must know your opponent if you plan to create an effective army. When planning a list that will compete with "all-comers", you will probably want to plan to play against MEQ armies (That's Marine Equivalent, for those who don't remember from earlier), but you can configure an army to handle a specific army too. I'm going to assume we're playing against MEQ for any math in this article.
What do you need to prepare for?
One decision you will need to make is what degree do you want to specialize your squads to handle different tasks. During a battle, you can generally divide your enemy units into four categories: Characters, Light infantry, Heavy Infantry/Light Vehicles, or Heavy Vehicles.
Characters are models with the Independant Character rule. They're often extremely deadly individuals, especially in hand-to-hand combat. This category also includes monsters like an Avatar, Hive Tyrant, or Daemon Prince.
Light infantry is any infantry unit with a 4+ or worse save. These are usually fielded in large numbers, making up for their individual weakness.
Heavy Infantry is infantry with a 2+ or 3+ save. Point-for-point, you will get less Heavy Infantry than Light Infantry, but Heavy Infantry will be better equipped and survive longer.
Light Vehicles are Vehicles with a front armour value of 10 or 11. These are usually transports or lightly armoured gunships (like a landspeeder). We use Front armour because no vehicles have worse frontal armour than side armour, and they're going to attempt to keep their front to you.
Heavy Vehicles are vehicles with front armour of 12 or better. I draw this cutoff as it is the point where weapons that are very good against heavy infantry or light vehicles (plasma guns, autocannons, starcannons) start to have problems scoring results on vehicles.
Most armies can field at least two of the above categories, and some, like marines, can field all five types of unit within their codex. So, in order to prepare for battle, you have to have a units that can be expected to address each type of unit the enemy will field.
To address light infantry, the most important factor is volume of fire, and, if possible, AP4 or better weaponry. Consider that a light infantry unit could be as many as 30 orks, and working backwards, they're not going to get saves, but a weapon that's strength 5 only wounds them 2/3rds of the time, so 45 hits will be needed, and with a BS of 3, that means 90 shots will have to be fired! At one shot per model, you're going to have a hard time with that. So you want to find weapons with a high rate of fire. Heavy Bolters, Multilasers, burst cannons, and even massed small-arms fire (bolters, pulse rifles, shuriken catapults, etc) will do the trick.
Heavy Infantry still wants some volume of fire, but with their saves, it's going to be a lot harder to kill them. The same 90 shots that take out 30 orks will only kill 10 marines due to their armour. So, for taking care of heavy infantry, you want quality shots. Strength 5 or better, with AP 3 or lower. These shots deprive the heavy infantry of their main advantage, their armour.
Against vehicles, the AP rating of the shot doesn't matter (except AP 1 weapons), only their strength. Any weapon Strength 5 or higher has a decent chance to hurt a light vehicle, while you really want strength 8 or higher weaponry to take care of heavy vehicles like tanks.
Characters are slightly different, in that you regularly cannot shoot them if there is a closer enemy unit, so defeating them in an assault is often the easiest means to attack them. However, most characters are also solid close-combat fighters, so this can be as difficult as getting a shot at them.
When designing your army and considering what to take, you have to decide whether to make generalized squads, capable of handling anything they encounter, or dedicated squads, each with a mission in mind.
There are advantages and disadvantages to each option, and often the best solution is a combination of the two approaches. Each different army in the game is designed with this question in mind. Armies like marines are designed to allow each squad to carry weapons that will allow them to handle all sorts of situations. While, at the other extreme, Eldar Aspect Warriors tend to be good at one thing, and average, or even bad, at other tasks.
Under this plan, you design each squad with a job in mind. You may have a close-combat squad, designed with power weapons, for taking care of enemy heavy infantry, a squad of tank hunters with anti-vehicular weapons, and a squad of troops with small-arms for handling any light infantry you encounter.
One advantage to this is that some armies naturally lend themselves to this approach. Both Orks and Eldar, specifically, have notably different units with different advantages versus different targets. With Eldar, for example, the aspects are a perfect example of this. You have your Howling Banshees and Dark Reapers for handling heavy infantry. Your Striking Scorpions and Warp Spiders for Light Infantry, and your Fire Dragons for vehicles.
Another advantage is that you know what your targets are before you start playing, and can deploy your strengths to meet their natural targets.
Finally, you end up with fewer wasted shots this way. If your entire unit is designed to kill tanks, then any time you shoot at a tank, you get to bring all your weapons to address the tank. None of your guys have anti-infantry weapons that are wasted firing at an armoured target.
On the other hand, having specialized units can lead to a few problems. If you have two units with tank-hunting capability and they're both disabled early in the game, then your opponent has little to fear with his tanks, and can move them at will for the rest of the game. Your opponent can attempt to neutralize the strongest threat to any given part of their force, and then use that portion of their force to wreck havok.
Also, the possibility exists that your opponent won't bring a specific kind of unit to the battle. A tank-hunting squad isn't going to be of much use against a horde army, and the points you paid for the anti-tank weaponry is wasted when there are no tanks to fire at.
The other end of the spectrum is the squad that is designed to be able to do a little of everything. Armies like Space Marines naturally lend themselves towards this approach, as every squad can purchase a heavy weapon and a special weapon, giving them a lot of flexibility.
The main advantages to doing this are flexibility and redundancy. If all your squads have one rocket launcher in them, then as long as you have a single squad left, you still have something that can hit your opponent's tanks. Your opponent cannot single out your tank hunters, as they're scattered throughout your army. Also, you don't find yourself in a situation where your tank-hunters are on the other side of the board from the enemy tanks.
But, multipurpose squads also have their drawbacks. If you fire your rocket launcher at an enemy tank, then all the other guns in the squad that cannot hurt the tank end up wasted for the turn. In a full marine squad, that can be as many as 18 bolter shots that cannot do anything, because the one marine with the rocket launcher needed to kill the tank.
This problem is compounded when you realize that one rocket might not kill the tank. A squad of marines with four rocket launchers have four chances to blow up the tank. Squads with one rocket each would need to dedicate four whole squads of marines to get the same odds of destroying the tank, and that means that the 18 bolter shots from the first squad are wasted, as are the 54 bolter shots from the other three squads.
Mixing dedicated squads with flexible squads
This can be a good compromise solution, but you have to be careful to get the mix right. Having one dedicated anti-tank squad, with three other units with one rocket each, means that as long as the anti-tank squad exists, they're the best choice to destroy the enemy vehicles. But, if they die, you still have some anti-vehicular capacity spread around the rest of your force.
You want to be careful to pay attention to each unit's primary and secondary role in this case, and make sure that you're not wasting too many points. A unit with the primary responsiblity to kill infantry, with a secondary role as emergency tank-killers, will want to select their weapons with their roles in mind. While a flamer might be a good anti-infantry weapon, it is at odds with the rocket launcher, as the flamer will require getting very close to the opponent to use, while the rocket launcher is a very long-range weapon.
You also want to pay attention to the cost of the various upgrades that allow a unit to do a secondary job. A dedicated squad of tank-hunters can benefit from the additional strength that a lascannon provides over a rocket launcher, but, the standard marine squad who want a weapon for just-in-case purposes may be better served with the rocket launcher because of its lower point cost.
While your choice of army will play a significant part in deciding to what extent your units will specialize or not, maintaining redundancy while reducing wasted shots is a good goal to strive towards.
What are the purposes of our various force organization choices?
"Battles are sometimes won by generals; wars are nearly always won by
sergeants and privates."
I put troops first because they're the most important part of your army. While they rarely have the speed of fast attack choices, or the hitting power of elites or heavy support, they're the solid, cost-efficient, all-around units that you cannot win the game without. It doesn't matter what point level you're playing at, you're going to get more bodies, more guns, and more units for the points you put into your troops.
These are the guys you order to take and hold objectives. They're not the glory seekers, they're the soldiers that have to be there to allow the glory seekers to go seeking glory.
As such, along with the requirement that you put 2 Troop units in your force organization, it's also recommended that at least 40%, and as much as 60 to 70% of your total points be invested in your troop choices. Afterall, if you do the bare minimum in troops, you're going to be stuck without units to seize objectives or take wounds.
Large squads or small squads?
One thought here is that you take large squads if you plan to assault, and small squads if you want to shoot. Why? Well, a large squad will have the bodies to absorb damage as it charges across the field. You want to arrive at the combat with enough bodies left to do some damage when you get there, so having a lot of bodies allows for that. However, when weapon upgrades are available, you are usually allowed a set number per squad. When this is the case, taking smaller squads will allow you to maximize the number of special weapons in the army. It will also allow you to attack more different targets every turn, preventing wasted shots. If the first small unit eliminates the first target, the second one can shoot something else.
However, the other approach is that you should always maximize unit size, as it gives significant longevity to any unit. A unit of five will have to make a break test after only 2 casualties, and again (at -1) for every additional casualty. A unit of ten has to lose three models before its first morale check, and another two before its second. The additional wounds will also help ensure that the points paid for special weapon upgrades survive long enough to inflict damage.
Both arguments have merit, and so its a decision you have to make for yourself, considering the role that you want the unit to play and the army you're playing. A horde style army wins via numbers, so maximizing squad size only makes sense. Marines are highly resilient and have solid weapon upgrade options, so minimizing squad sizes to get extra weapons is worth it.
A final note on unit size: Under 4th edition, it is almost universally better to take squads with an even number of models than an odd number, and non-multiples of four are best. This is because units have to be reduced below half their starting size to no longer count as scoring. That means that a squad of 7 no longer counts as scoring if it takes more than three casualties, while a unit of six can also withstand three casualties and still count as scoring. The seventh model does not actually provide an extra scoring body.
Furthermore, you also have to take your morale tests based on losing 25% of your models. That means that if you want to be able to take one casualty without needing a test (or, put another way, if you want to make your first test based on losing two models), then your unit size has to be 5, 6, 7 or 8 strong. The following table sums this up.
As you can see, you get increases in casualties required to non-score your units on even numbers. This is the most important thing, so we then ignore the odd squad-sizes, and notice that the increases in casualties taken before needing a morale check happen on the non-divisible-by-four sized units. (6 and 10). So, to optimize the wounds in a squad, you want to run squads of 6, 10, 14, 18, etc.
HQ & Elites
"Win with ability, not with numbers"
HQ and Elites often serve the same purpose. These are units that you want to use to attack your opponent with, to take away their objectives, or destroy their plans. They're usually able to produce a greater offensive threat than your troops, while their increased cost ensures that you won't be able to field as many. The combination of these factors means that these units should be used offensively, to deal as much damage as possible. Using elites or HQ models to take an objective is wasting their offensive capabilities (they'll just sit on the objective once they have it), and will be more vulnerable to enemy attempts to take the objective back due to their natural smaller unit sizes. That isn't to say it is never effective to take an objective with an elite unit. Certainly if there's a point to be claimed near the end of the game and you have an elite in range to take it, do so. But realize that this isn't the strength of these unit types. HQ and Elites usually have the best access to the armoury, allowing them to buy weapons and equipment. While it can be tempting to build super-characters or units, remember the addage about eggs and baskets. In general, you don't want to spend more points on elites or HQ than you have spent on troops.
"Without cavalry, battles are without result"
These units are, as their name implies, your most mobile units. Their job is the most likely to change as the game progresses. Early in the game, you will want to use these units to make early attacks. If your army is assault-based, you will want to get them charged into something to lock it in place, allowing the rest of your force to catch up. In the middle of the game, they're most useful harrassing the opponent's flanks, or closing on their Heavy Support units. At the end of the game, their mobility comes in useful by allowing them to move to claim or contest objectives. These units are often fragile, or lacking in firepower, but these are not their strength. They don't want to sit around waiting to be shot, they want to be moving, causing disruption in your opponenet's plans.
"A battery of field artillery is worth a thousand muskets."
These units serve as your firebase. They're rarely very mobile (although there are some exceptions to that), and they deploy first, so you have to take care when deploying them to put them where they can do damage, without taking a lot of fire in return. While their offensive output is significant, they're usually either more expensive than your troops, less mobile, or both. It is tempting to load up on heavy support choices, but this isn't advisable, as maintaining balance, and remembering that the core of your army is its troops will win more games in the long run.
How to decide?
"The side with the simplest uniforms wins."
Now we get to the meat of figuring out what to include in your army list.
For every army, there are choices to be made. Some armies have more choices, but choices exist none the less. And, each choice comes with an associated point cost. The points have to be made somewhat generic, so that all armies balance (mostly) with each other. But, that means that against specific targets, different options will be more or less effective.
Lets do a quick example. You are playing eldar, and have 100 points to spend on a Guardian Squad. For those points, you could buy either 12 guardians, or 6 guardians and a starcannon, or 7 guardians and a scatterlaser, or 6 guardians and a brightlance.
You're playing versus marines. Marines, who you don't expect will be bringing any heavy vehicles. (It's a low point game). What is going to be the best return on your 100 points?
We can examine that mathematically.
There are three distinctly different ranges involved. Over 36 inches away, no one in the squad will be able to do anything. Between 12 and 36 inches, the three heavy weapon options would be able to fire, but not the guardians. At under 12 inches the whole unit can fire.
The table below will show the expected results of one round of firing at marines for each selection.
As you can see, the starcannon option has a signficantly higher expectation against marines, at both long and short range.
Against Orks, however, the results are slightly different:
Since Orks have no real armour to speak of, the advantage that the starcannon offers (the low AP value) is lessened, as all the eldar weapons will deny the orks their save. In this case, at long range, the Scatterlaser, with it's higher rate of fire, wins out, while at close range, simply buying more guardians is more effective.
What to plan against
There's a reason that most of my examples use marines as the target. Marine Equivalent armies are the majority of all 40k armies. There are almost as many individual marine chapter codicies as there are alien codicies. (Ultramarines, Blood Angels, Dark Angels, Black Templars, Space Wolves - Eldar, Orks, Tau, Necrons, Tyranids, Dark Eldar). Necrons count as a Marine Equivalent army (same statline), and then there are the Chaos Factions, all also based around the Marine statline.
So, if you know what you're going to play against, go ahead and choose the most efficient options to handle that enemy. But, if you don't know what to expect, picking weapons that are effective against marine stats isn't a bad idea. If you do know who you are facing, it helps to know what their units are like, to help you pick the most effective weapons.
Keep in mind, however, what was discussed before, about roles for units. If you're planning on throwing a unit of guardians into close combat, buying them extra shooting power is probably a waste of points.
A lot of efficiency issues can be determined empirically through play. If you paid points for something and it just doesn't seem to be effective, it's probably not the most efficient thing you could have bought. But, it is more valuable to know before you invest in buying or converting the models in question.
Picking the right unit for the job
This is another efficiency issue. You need a unit to do some vehicle hunting. So, you have to consider what? Can the unit get in range of the tank? Can the unit reliably penetrate the armour of the tank? How close does it have to get? How quickly can it get there? Are they likely to survive to deal damage? Sometimes, you have to size up the possible options and decide which you want to go with based on the pros and cons of each option.
As an example comparison, we can compare roughly 180 points of Tau anti-tank options.
How quickly can we get in range? Option A is either in range or not. The railguns have range to most any target they can see, so the biggest drawback here would be terrain issues. If you can resolve those, you're good to go. Option B can either deepstrike near the tank, or can move up to 12 inches a turn to get there. They need to be at most, 12 inches from their target, and ideally, under 6 inches away. Option C, like option A, has significant range, but unlike option A, the hammerhead can move a full 12 inches and still fire, so it can redeploy itself as the game progresses to get better shots.
How likely is the unit to survive? Option A has four wounds, a 2+ save, and a 4+ invulnerable save. They're also going to be operating at range, avoiding a lot of enemy fire that way. They will probably get their shots at whatever they're deployed to attack, but may then have to move to address any additional targets. Option B has six wounds, but has to get in close to the enemy, and only has a 3+ save. If they're forced to walk (fly) to their target, they're going to take some hits on the way. If they deepstrike near the target, they'll get at least one round of shooting, but risk deepstrike misses, and will possibly be stranded behind enemy lines. Option C has good armour, especially if it keeps moving. But, one lucky shot can down any vehicle.
How reliably can they penetrate enemy armour? Option A has 2 twin-linked shots with BS3. They should score 1.5 hits. Out of those hits, they automatically penetrate armour 10 and 11, and have a 50% chance of penetrating armour 14. So, they can expect .75 penetrating hits per turn firing at armour 14. Option B has 3 twin-linked fusion shots, and 2 missile pod shots. That averages 2.25 fusion hits, and 1 missile hit. If they get within 6 inches of the target, they're auto-penetrating armour 10, and have a 72% chance to penetrate armour 14. They can expect 1.62 penetrating hits per round shooting. In addition, by deepstriking, they have the potential to shoot at weaker rear armour. Option C has one railgun shot, so will score .66 hits. With a 50% chance of penetrating armour 14, it can expect .33 penetrating hits per turn firing.
Which is best? For the chance to blow up an enemy tank early in the game, the broadsides are clearly the best option. They can be deployed with shots at their target, and have a high expectation of getting positive results when they fire.
But, their use diminishes as the game goes on. They have to get their hits in early or the enemy will out maneuver them.
Option B is the best mid-to-late game option, as they can arrive where you need them, and engage the rear of the tanks with some heavy anti-tank fire. But, they're likely to be stranded after that one initial strike, without much in the way of support.
Option C is an ok choice, but severly lacks in potential compared to the other two options. It just doesn't have as many shots to get the hits it needs to be reliable. But, it will most likely effect more of the game. It can fire in the early turns, like the broadsides, and is also maneuverable enough to still pose a threat in the later game.
Note, there isn't a "right" choice in this example. It's intended more to show you how to make the decision, than to claim that one option is always right. It comes down to personal play preferences. Do you want to hit early? Are you willing to wait for deepstrike rolls? Are you willing to trade a little reliability for overall longevity?
Part of the cost for adding anything to your army includes the things that you are not adding, that you could add for the same points. The cost for a marine to buy a missile launcher is 10 points. A Heavy Bolter costs 5 points. What are you getting with the 5 extra points? Fired at marines, a Heavy Bolter will inflict .44 unsaved wounds per turn, while a rocket launcher will inflict .55 unsaved wounds per turn. Over the course of six turns, if you fire every turn, that's .66 more dead marines with the missile launcher. .66 Marines cost you 10 points, so the missile launcer is 10 points more effective over the course of a game than the heavy bolter. But it only costs 5 points more. Why is this?
Well, first, what are the odds that you will get to fire it every turn? If you only fire it three turns, then it only nets .33 more marines than the Heavy Bolter, which is exactly the 5 points more than it costs. What does that tell us? It says that, in order to justify the cost of the rocketlauncher, it has to fire at least three times in the game. It doesn't necessarily have to hit each time (3 shots = 2 hits with marines), but if you are going to pay the extra points for it, you had better use it. The 10 points spent on the rocket launcher are wasted points if it doesn't fire at least three times. And that's just compared to the heavy bolter.
Of course, sometimes, the advantage of having something is not having to fire it. If the addition of the rocket launcher means that your opponent keeps his tank out of your marine's way, then that's 10 points well spent, even though it never fired. But, in general, if you're going to pay points for something, you had best make good use of it, or you might as well have spent the points on something that you will use.