Simply put, a formation is the way in which an army is deployed on the battlefield. There are many different ways to deploy an army, some are more effective than others in a given situation or against a certain opponent. In all the time I've been playing 40k, most of the formations I've seen can be categorized in two broad types, the 'phalanx' and the 'flank attack'. The following pages will have some illustrations showing variations on these two formation types, but for now here are a few things I think are important to know about battle formations in general:

Battle Line: Due in part to the shape of the deployment zones in most 40k missions, most armies tend to form a 'battle line' of sorts. Units are placed side by side in support of one another, presenting a broad frontage to the enemy. If this seems pretty conventional, that's because it is. The game of 40k was translated over from Warhammer Fantasy which represents battle in a 'historical' way, with ranked troops and so forth.

Flank: The flanks of a formation are the units on either end of the battle line. Since they don't have as much support as units in the center of the line, they are more vulnerable to attack. One thing that every battlefield commander fears is being "flanked"; i.e. having an enemy outmanuever you, hit you in the weakest part of your formation and then start "rolling-up" your line. Historically, the effect of a flank attack on troop morale was devastating, causing confusion and panic. Such attacks usually spelled defeat for the army being flanked.

Mobile Force: Most armies generally contain specialist units that have the edge in mobility over the basic line trooper. These units use their speed to launch raids into enemy lines and hit your opponent where he's weak. There are a few armies out there that contain few, if any, mobile elements, but they are the exception rather than the rule. There are also some players who build their armies without mobile forces, but this is usually a matter of preference.

Fixing Force: For a mobile force to be able to operate effectively, the enemy needs to be stationary or at least limited in it's mobility. This is the job of the "Fixing Force", units whose purpose is to engage the enemy battle line and hold them in place while the "Mobile Force" swoops in and does it's thing. "Fixing Force" units can accomplish this in a number of ways. I've seen it done with assaults, close-range firefights, pinning weapons, etc. Heck, even just by presenting a big scary block of troops, some opponents will concentrate on the "Fixing Force" instead of the much smaller mobile elements.
 

In military terminology, an enemy's 'Center of Gravity' is defined as:

"a source of 'massed strength' - physical or moral, or a source of leverage whose serious degradation, dislocation, neutralization or destruction will have the most decisive impact on the enemy's ability to accomplish a given military objective."

In 40k terms, the "Center of Gravity" is the point in a battle formation that will cause the most mayhem if taken out. A good example of a "CoG" would be heavy weapon teams accompanied by some basic line troops and a command unit who provide protection and leadership. Placed in a position of heavy cover with good lines of sight to the battlefield, this collection of units can make a resilient and effective firebase.

Such a firebase can provide supporting fire for an entire army but represents a substantial investment in resources. If it can be destroyed, the army will lose not only it's fire support but a fair chunk of it's manpower as well.

Not every player will deploy their army in such a way as to have an obvious "CoG", preferring instead to have a dispersed formation. While deploying your army like this can deprive your opponent of an obvious target, it can also deprive you of a 'strongpoint' to fall back to. Having said that, it can be very effective to have a firebase in your deployment. Just don't put all your eggs in one basket!

A "CoG" can also be abstract as well, it doesn't neccessarily have to be composed of enemy units. It just needs to be something that is valuable to the enemy and will cause him serious problems if it is destroyed or captured. In many 40k missions, victory is determined not by the casualty ratio but by controlling objectives. In these cases, the "CoG" will probably be a specific area of the battlefield, regardless of troop concentrations.

Accurately identifying your opponent's "Center of Gravity" and coming up with a plan to either destroy or capture it is the key to winning games effectively. Once you have control of the "CoG", or are in a position to take control of it at you leisure, you can then worry about mopping up the rest of the enemy. If you concentrate on destroying the enemy first and worrying about the objectives later, you run the risk of going 'kill crazy', losing sight of the mission objectives and potentially losing the game. Remember, keep your eyes on the prize!
 

As I said before, it's best if you deploy your army according to a battle plan. If you know where you need to go and what you need to do, you will be more able to move and attack in a coordinated fashion, and your game will flow smoother. For the first turn or two at least.

By having a plan, you can take the initiative in a battle and force your opponent to react. If you don't, then you'll be reacting to your opponent's movements, and you have conceded control of the game. This...is...a...BAD...thing! By giving control over to your opponent, he will have an edge. Your opponent may very well take control of the game, it happens, but don't just give it to him. Make him work for it.

"No battleplan ever survives contact with the enemy"
                                                                        - Field Marshall Helmuth von Moltke

Remember, no matter how perfect you think your plan is, ALWAYS have a backup. A wargame battle, like a real one, is a highly fluid situation. Your opponent will do things you won't expect. He may not fall for your cunningly laid trap, or he may pull a manuever that catches you completely off guard. Sometimes you need to hold to your plan in the face of the unexpected, other times you may need to change your tactics. How can you tell the difference? Practice.

If you have a plan going into the game and your opponent doesn't, then you will move and attack with purpose, making it easier to control the flow of the game and this will give you an edge. Games like this are generally pretty one-sided and the outcome of the game can usually be determined pretty early on.

If neither of you have a plan going into a game, things may very well end up looking like an episode of the Keystone Cops. Things may get done, but it won't be pretty.

If both you and your opponent come to the table with a plan, it will come down to who can execute their plan most effectively. Control of the game may shift back and forth, and the game may hang in the balance until the last turn. If this happens, consider yourself fortunate, you have found a worthy opponent. Games like this are the most challenging and enjoyable. They can be nerve-wracking while you're playing, but you will remember them for a long time. Some of my favorite games, win or lose, have been "nail-biters" in which you couldn't tell who won until the very end.
 

Remember when I talked about the advantages of going second? Well, here's where it really pays off. If you deploy first, you put your whole army on the table without knowing what your opponent might have up his sleeve. Essentially, you're going in blind... well, half-blind anyway.

In cases like this, your battle plan and formation will probably be somewhat generalized. You'll be able to see the terrain and any battlefield objectives, and can make plans to move and capture them. But since you don't know exactly where the enemy will be, any plans to take them out will be guesswork at best.

By going second, you get the full battlefield picture. You get to see the terrain, objectives and where the enemy has deployed before you drop a single model on the table. This makes a HUGE difference when coming up with a battle plan. You can see exactly where your opponent has placed his forces in relation to the objectives and can probably get a good idea of what his plan might be. You can then formulate your battleplan to counter his, and place your forces in position to take advantage of any weak spots in his deployment. Since you also have full knowledge that your popponent will take the first turn, you can position your forces so they are protected from the worst of the enemy's firepower.

By having your opponent show his hand first, you will be in a better position to counter his battle plan and accomplish your own goals.
 

I've been going on about battle plans and their importance for a while now. Why it's important to have one, and what can happen if you don't. By now you're probably saying "This is all well and good, but when the hell is he going to show us some of these fancy plans?"

Well folks, the wait is over...