Back to Basics: Multiple assaults in Warhammer 40,000 - Done correctly

I think this is one of the most misunderstood aspects of the game. Even normal assaults a lot of people don't get which means people are unable to protect against or properly setup multiple assaults. This is going to work in conjunction with my post on how to break bubblewraps but for now let's make sure we all understand how a bog standard assault and multiple assaults work. Let's head to the rulebook and look at some important rules. I'm going to paraphrase.

1. A unit which takes a difficult or dangerous terrain test strikes at I1 unless the unit has assault grenades or all of the intended targets were either already engaged in combat or had gone to ground. If the unit doesn't take a test (even if the opposing unit is in terrain) the models strike at initiative!
2. The 1" rule is ignored during assaults but models still cannot move through other models, impassable terrain or areas where there base would not normally fit.
3. The closest model must initiate the assault followed by any Independent Characters. Otherwise the order you move them in doesn't matter but they must meet the normal assault rules.
4. All models must try and engage an un-engaged model and if unable to do so, come into base to base contact with an engaged model and if unable to do so, be within 2" of a model in base to base contact with an enemy. This means you cannot string units out to avoid combat but units which are unable to get into base to base contact can be 'left behind' as long as they are within 2" of engaged models (if possible).
5. If none of the above is possible the models must stay in coherency. This is very rare unless you string out before the assault.
6. The unit must stay in coherency (this is the biggest doozy against multiple assaults) when engaged in combat. This is particularly important if you are trying to engage certain models with certain models of your own.

This is for the attacker. Some other basics we need to understand. Independent characters for all intents and purposes of allocating attacks are separate units in combat unless part of a retinue. However, if the character was attached to the unit before the assault they are treated as one unit for combat resolution (i.e. only make one roll). Remember to allocate attacks against the character if you wish to and don't roll saves for the character unless it was targeted! Furthermore, ICs must move first in defender react moves and must get into base to base contact if possible. Remember with the new FAQ ICs also push other models out of the way to ensure they can engage the opponent. You have been warned.

Here we have an infantry platoon about to be assaulted by some Assault Terminators with Lightning Claws (i.e. killed). The IG player has setup their infantry to protect the HWT and since there is no way through or around the unit, the Terminators must assault the infantry platoon like so.

 As we can see, the Terminators are all within 2" of each other and thus have made a legal assault. However, the order in which they move is very important as well as each must end their move within 2" of an engaged model (other than the first). Let's take a look at another example.

Here the IG player has made a mistake and there is a gap a terminator can fit through to engage the HWT behind. However, the Terminators must obey the assault rules to be able to effectively access the HWT behind. Whilst there is a direct line for one of the Terminators to engage the HWT, if the intended target was the Infantry platoon (let's say they shot their laser eyes at the Infantry platoon) then that Terminator cannot charge as he is not within 2" of another engaged model. However, if the far right Terminator moves to engage the infantry platoon first whilst still leaving a gap for the other Terminator (remember, the 1" rule can be ignored now), the Terminators can also engage the HWT. The two pictures below outline the incorrect way to assault the the HWT and the correct way.

So what does this tell us. Timing is very important. Which model you to engage with immediately after the closest to closest move is very important as it will generally allow or disallow multiple assaults. This is particularly true with units who have very large assault ranges as they can stretch themselves out to engage another unit. Let's look at an example with some Raveners then who have a 12" assault move.

 Once again we have our assault unit lined up against an infantry platoon (they shot at the platoon with their thorax stuff) but the HWT are now off to the left. The HWT are easily in the assault range of the raveners on the left but the assault rules must be obeyed and the unit needs to stay within coherency. If we simply moved Raveners 1 and 2 up as normal to engage the Infantry platoon and try to let Ravener 4 engage the HWT it might be out of range as seen here.

 However, if we move Ravener 4 first to engage the Infantry Platoon on the left of Ravener 3 (remember, you just need to engage a model if possible and stay within coherency) we get enough coherency leeway to allow Ravener 1 to engage the HWT.

 This is where protecting against multiple assaults comes in from. If your units are all on one 'plane' it's really easy for assaulting units (particularly fast ones) to spread out to the sides and engage units in multiple assaults. The same goes for punching holes in protective units. Remember not to remove models which allow a base size through (the 1" rule is ignore during combat) otherwise if your units are too close together, multiple assaults will become common practice. Here is an example of how having your units on different 'planes' can protect against multiple assaults. All the units are setup the exact same but the HWT are moved 2" backwards and Ravener 1 is unable to engage them.

Getting multiple assaults off is quite difficult unless units are bunched up and quite close to each other. Even beast units with a 12" assault range are going to find it difficult to access multiple units on multiple planes whilst satisfying all of the assault rules. As a player you must remember this to protect against multiple assaults. Whilst blocking infantry with infantry in assault is harder than in movement due to the 1" rule being ignored, simply moving units forwards and backwards a couple of inches can make engaging them all at once much more difficult. The angle of the attack must be considered as well. In the above example with the Raveners if they were coming in from the left they would be able to engage both units quite easily even with them both being on different planes. Here it becomes important to simply have your units more than 3"-5" apart as it becomes physically impossible for units to engage them all at once depending upon their bases size.

So remember the assault rules and make sure your opponent does to but above all else remember that it is generally in your own movement phase when you setup multiple assaults for your opponent. Sometimes this is unavoidable as you've run out of room, have been forced to disembark, it's tactically important (i.e. an objective), etc. but don't present your opponent with opportunities they don't deserve.