This may very well be the best formation in the new Dark Angel codex (and perhaps the best formation available to any Astartes faction, with the possible exception of the Skyhammer Annihilation Force).
So, what does the Ravenwing Support Squadron bring to the fight? Well, first of all, it is made up of 3-5 RW Landspeeders and either a RW Darkshroud or a RW LS Vengeance. All of these models are combined into a single “super-unit” of 4-6 Land Speeders.
Outside of this unique grouping, the formation also gives all its modesl Grim Resolve (so BS2 overwatch, which usually vehicles do not get), Interceptor, Strafing Run (so BS5 when shooting against basically any non-flyers/FMC units), and the Ravenshield special rule. Ravenshield allows this formation fire overwatch in support of any friendly Ravenwing unit that is within 24″ of it. Combined with BS2 overwatch (from Grim Resolve) or even Overwatch at full BS5 (from being part of the Lion’s Blade and getting Supreme Fire Discipline rules), this makes for a highly effective defense against RW units being charged. Note that, since this formation itself is made up entirely of RW units, it can choose to fire overwatch when it is charged itself!
Beyond the Overwatch shenanigans, I think where the RW Support Squadron really shines is in two areas:
1 – The ability to attach a Darkshroud to a unit of RW Land Speeders. This means that the entire unit gains Scout and Shrouded from the Darkshroud (both of these abilities confer to the entire unit if even just one model has them). This means that, if the formation Jinks, it has a re-rollable 2+ cover save every time. If it does not, then it at least has a permanent 5+ cover save, which can be increased by hiding in terrain, potentially even providing the a 2+ cover save without moving/jinking (say the unit hovers behind an Aegis Defense Line). Addiing Scout to formation just further enhances its versatility, allowing pre-game mobility or the option to Outflank and come in turn 2 for shots against enemy weak side armor.
2 – The ability to use BS5 Interceptor shooting. With Interceptor ability being quite rare, especially for Astartes armies, this is invaluable addition to either a Dark Angel force or as an allied supplement to another army. If you kit out the RW Land Speeders with Cyclone Missile Launchers, then you have between 6-10 BS5 Krak Missiles with Interceptor, plus additional Heavy Bolter fire from this formation. Against deadly DSing opponents, such as D-Scythe Wraithguard with WWPs or Skyhammer Annihilation Force troops or Farsight Battlesuit deathstars, this can be a complete game-changer, potentially eliminating these dangerous threats before they even get the chance to engage your army.
Even if you don’t use the Interceptor and Overwatch special abilities, just having multiple Speeders with long range, Shrouded, and BS5 (which can be boosted by Prescience to give them 97% accuracy when shooting), this formation is highly versatile, surprising durable (thanks to the Dark Shroud), and provides a potent firebase for your army.