The Dark Angels are governed by 2 major rules that make them play differently from the Codex Chapters. These are "Stubborn" and "Intractable".

All Independant Characters are "Stubborn" due to their induction to the Inner Circle. This means that they automatically pass all morale checks, even against opponents that would normally cause a unit to automatically fall back. This attribute can also be conferred onto Veteran Sergeants as well. What this means is that Dark Angels will virtually do everything that the player wants them to do. In that sense, they make perfect defensive troops, and will defend an objective to the last man if necessary.

"Intractable" comes into play when squads that are not "Stubborn" (possibly due to un-upgraded Veteran Sergeant or loss of Stubborn Veteran Sergeants) fail a morale check due to 25% shooting losses. They do not fall back, and cannot move or assault in the next turn, although they can still shoot as normal. Note that this applies only to losses incurred by enemy shooting, and does not cover assault losses. So it is still possible to make them fall back through winning an assault. Deathwing and Ravenwing units are exempt from this rule.

The combination of these two rules make a Dark Angels army very difficult to shift or break. It also means that you get an army that is as relentless as possible on the attack this side of Tyranids :) With the update in (Oz) WD 266, Dark Angels Tactical Squads can be equipped with Plasma Cannons, so expect this weapon to be the one of choice when facing Marine armies.

This makes weathering Dark Angels firepower particularly difficult and they are ideal against Assault-focused armies like the Blood Angels and Tyranids. All their squads will continue to keep shooting at you unless you're engaged in close combat with them or they can't see you. That means you need to make the most of whatever cover you can get to minimize this level of firepower. Having said that, they are not as shooty as Tau or Eldar, and they are fairly strong in the assault as well. In general, expect one Assault Squad tasked with a counter-assault role just behind the main firing line.

When they bring the Deathwing and Ravenwing into play, things become more complicated. The Deathwing has all the attributes mentioned above, and are also capable of having assault weapons in a shooty squad. When faced with one of these, possibly the best option is to assault them and hope to take their numbers down. If you allow them to assault you and strike simultaneously, things can get messy very fast :)

Ravenwing units are likely to perform deep sorties into your lines to engage the second wave of your assaults or any supporting units, thus isolating the forward assault wave. With the ability to re-roll difficult terrain tests, these guys on bikes will pop out from just about anywhere. Also, the Ravenwing Landspeeders, while optimized against lightly armoured troops, are still deadly in the amount of firepower that they can dish out (3 Landspeeder Tornados with Assault Cannons and Heavy Bolters... count the dice).

I would reckon that the usual tips against shooty armies are definitely useful. Deep striking is definitely an option to disrupt his shooting, although that does represent a gamble to a certain degree. Your assault will definitely get bogged down so do not expect your assault elements (exept for those with Power Weapons like Honour Guard) to cut through them in one turn. Support is vital... especially getting your second wave across the board ASAP into close combat. You will need to play it close to them. Sitting away only gives the Dark Angels more time to whittle down your troops. Playing against Dark Angels requires patience in using cover on your part and the ability to hit really hard when needed to. Hope this helps :)

article courtesy of Interrogator Chaplain Ignacio