While Chaos Space Marines have decent air defense in the form of Heldrakes and their Vector Strikes, they are otherwise pretty limited in their options against flyers and FMCs. They also have some decent options in close combat, but many of their “elite” options (i.e. Possessed, Mutilators, etc.) are decidedly second-tier for their points cost.
One combination available to Chaos Space Marines to mitigate both of these issues is using the much maligned Warp Talons in conjunction with a fortification, like the Firestorm Redoubt. If equipped with 2 x Quad Icarus Lascannons and the upgrade to make their shooting BS3 (which means 4 Lascannon shots, hitting 75% of the time due to BS3 Twin-Linked), this gives Chaos a very solid “base” against flyers, FMCs, and Skimmers, especially since these weapons also have Interceptor to help them engage oncoming Reserves.
So, where do the Warp Talons come in? Unlike vehicles, buildings can embark Jump Infantry and the Firestorm Redoubt can hold 20 models (or 10 Bulky Jump Pack models). Combine this with the ability to upgrade with an Escape Hatch (can be placed withing 12″ of the building before the game and acts as a “free” access point, just without the ability charge when you disembark from it) and you suddenly have the ability to “catapult” 10 Warp talons between 19-24″ accross the board turn 1… i.e. Firestorm Redoubt is placed along the edge of your DZ… Escape Hatch is placed 12″ from Firestorm redoubt, in the direction of your opponent’s DZ… Turn 1, Disembark Warp Talons out of Escape Hatch up to 6″, then run another D6″… that nets yous the 19-24″ in one turn, setting the Warp Talons up for an easy Turn 2 charge using their 12″ move Jump Packs. Of course lack of grenades and terrain is a danger to them, but against the right units (say you gave the Warp Talons Mark of Khorne), you have 41 x S4 AP3 attacks, all with Shred. That will wipe out almost any MEQ or GEQ unit out there and will even do decent damage to TEQs (41 attacks, about 20 hits, about 15 wounds, and 2-3 dead Terminators).
More importantly, it puts signficant turn 2 pressure on the enemy DZ and also allows you the opportunity to snap up objectives with the Warp Talon’s great mobility. Of course, this combination is not going to hold up all by itself, but it can really round out the rest of your CSM army, providing anti-air, close combat, and mid-field control options all in a solid package.