Blocking is a quintessential skill in 40k (and Fantasy but we'll focus on 40k here) and we've discussed it's most basic of uses before. By using vehicle hulls and infantry models (i.e. bubble-wrap) combined with the 1" rule in 40k, you can impact significantly on your opponent's ability to control the battlefield through movement. The most direct forms of this tactic are delaying opponent's reaching your lines (especially assault based armies or units like Blood Angels and Terminators) and forcing an assault on a particular unit, etc. Whilst it can basically be summed up as "throw unit forward to block other unit's forward movement as much as possible to defend against scenario x" there is a lot more thought required to go into that. This article doesn't look at that :P (Ha! I had you all fooled) as it was covered to an extent in the previously linked article. I also assume you can extrapolate when it's a good idea to blindly rush forward and block a Land Raider and when it's not a good idea to blindly rush forward and block a Rhino...
So what does this article look at? The above type of blocking is very much 'offensive' in nature. Yes it's primary purpose is defense for the rest of your army in controlling your opponent's movement but the blocking unit often goes out there and stops an enemy from getting close to you (I am not including bubble-wrap here). There's nothing wrong with this and some armies and units use it extensively (i.e. Tau with Piranhas). However, there is more to blocking than just this! What I'm about to explain is called defensive blocking and rather than having the blocking units move out to disrupt your opponent, blocking units directly allow other units to be more effective. For example, in this picture here from my Round 4 game at Lords of Terra, the Raveners (who cannot assault having just deep struck) have moved within 1" of the ASM. This means all of the ASM cannot pile into the Gants when they assaulted. Whilst this isn't a great example as the ASM are all clumped up, doing this on a spread out unit or against particularly large units can extend combat (which is often very useful) or stop a unit from being wiped out.
The Raveners claw at the air...
This is great and all but we can go further with tanks and stopping assaults cold. What this is based around is often called the tri-rhino (seen below) and aims to protect a unit but still allowing it to shoot. What this does is completely stop assaults on the unit unless a tank is exploded as the hulls of vehicles do not leave a gap big enough for a model to pass through but thanks to the design of tanks, allow the unit to shoot out freely. With some precision movement this can be done so one Rhino moves >6" (and is the lead tank to accept charges) and unloads its cargo whilst the other two move <6" so they can fire from the top hatch. This can also be used with units like Razorbacks and is particularly effective with Blood Angels RBacks and Immolators as they can move 12" and still fire their weapon. Bust a tank with melta and stick some templates on them. Fun times.
Let us hide with our awesome 3+ armor!
Now the great thing about this is your unit can basically fire on a tank with impunity and is only vulnerable to return shooting yet still gets a cover save whilst generally not providing one your opponent (assuming you deploy the 'mouth' of the Rhinos correctly. See the picture below for a clear 100% LoS view of an opposing Predator.
Head shot.
So the unit is protected from assaults, gets cover from shooting and has clear LoS if you aim the 'mouth' correctly and you can get within melta range for meltaguns. What's not to love about this setup? Well it's difficult to employ. Maneuvering three Rhinos and unloading a single squad is difficult at best and is a steep investment for protecting a single squad and leaving the Rhinos generally in the open. With faster armies like BA or units like Immolators which can move 12" and fire it's a lot easier to pull off as you can maximise your firepower whilst moving up to 12". However, this doesn't mean it's useless and can be very effective against horde assault armies as you can protect your units and tank shock out of assaults (using flamers instead of meltaguns obviously).
There are also more feasible applications by using less chassis and just creating a V (see pictures below). This obviously leaves the unit open to assaults from behind or units wrapping around the tanks and engaging the infantry unit but is a lot easier to pull off and more feasible. You can also deploy backfield tanks in a similar manner to protect long-ranged infantry against assaults or to provide cover, etc.
I don't have a stupid witty comment for this one.
Whilst not exactly ground breaking, this is a different from of blocking. Rather than having designated units slowing your opponent down, you are protecting units from assaults directly and allowing units to disembark. You'll often hear me say you should rarely jump out of your transport and this is true, you've paid for the protection, why sacrifice it? However, when you jump out correctly into a protected space (i.e. the examples above) you gain mobility in terms of being able to move 12" and fire what you'd normally fire from the top-hatch and are therefore putting pressure on your opponents. This can also be done with other armies in different ways such as Eldar/DE/Tau with skimmers and shooting under them but their transports are often significantly more expensive. Furthermore (and this is huge), this also allows you to see your pretty models rather than the boxes they travel in ^^.
There are more applications of this type of movement blocking such as assaulting a unit and protecting it with a metal bawks (similar to the Ravener example above), shuffling units in particular directions, etc. and I can do further posts on them if desired.
