The stormraven is a new piece of kit, unlike more established vehicles there is little guidance about it. And its something that adds something not found so often in the Grey Knights... speed. So lets look at the options.
Urban Assault VehicleThe obvious use, costs less than a land raider, carries about as much plus a dreadnought for good measure. Flying into people's faces and dumping everything is surely worth a giggle. It's increased toughness against melta weaponry is nice in a melta dependant 5th edition world and makes it harder to deal with at close range than a land raider... the flipside is that you're more vulnerable when the odds are more even. Armour 12 is a long way from the confidence that a 14 all around armour value gives you when steaming though enemy firepower.
You're paying twice as much to bring a Stormraven to the party as the IG do for their Valkyrie, and you're not much tougher. On advantage the Grey Knight version has over the Blood Angels is the psychic power to ignore lighter damage, keeping moving and keeping firing is worth every penny. Given the machine spirit will keep you firing when moving at high speed its worth asking yourself why you wouldn't want the cover save when you have a chance to grab it... the extra defence from travelling flat out could keep your Stormraven in the game.
Drive Closer, I want to hit them with my Nemsis Force Sword!Sure you do! And thats a great plan. But lets put some thought in what you want to carry. Throwing all your eggs in one basket is well known as not being a great plan... generally you want something effective to make it worth using an expensive transport to deliver them its a difficult balance. On top of this you're probably going to want to hold an objective once you arrive... while its perfectly reasonable to simply field a hammer unit whos job it is to go an beat units flat it means you'll need to send someone else to pick up the objective.
Terminators and Purifiers are likely to be good candidates for going it alone, the immense combat power and resilience of Paladins is worth considering although you pay for their skills to be deployed.
A Librarian is a good option, using the Stormraven's speed to push him into position you can summon more squads to his location... this advantage in speed is probably good reason to take a dreadnought along for the ride simply because you can and getting dreadnoughts into the thick of the action where they can punch stuff is real hard without drop pods like the vanilla marines.
If you prefer to keep it cheap, its worth considering an Inquisitor's Henchman unit. With wildly differing abilities and weapons you can set them up to do any job. More anti-tank in the form of meltas, or high combat offence with assassins the only real limit is trying to do everything at once.
Open fire. All weapons!As an actual gunship the Grey Knight's Stormraven is somewhat lacking, you basically have two main weapons, a few frags with intresting rules and the option for hurricane bolters. Not much point in lamenting over the Blood Angels getting a one off anti-tank punch capable of knocking out a squadron of hydras so lets look at the weapons available.
On the chin? Multi-melta, when it comes down to it, its hard to justify putting anything else in the nose weapon slot. Between the the facts it costs you nothing, is highly accurate and is arguably going to be one of the best anti-tank weapons you'll get your hands on its no contest. The missile launcher isn't exactly a bad weapon bad, its just that its going to struggle to be as good and costs extra.
On the top? All the options are free, and to be honest they're all good options. Its one of the few places you have access to Plasmacannons which is a vote in their favour, on the other hand its also the case that the area you struggle in with anti-tank so the lascannons win out in my book.
Consider that with the machine spirit you can fly 12", fire the multi-meltas at one vehicle and laser another with the computer to try for a cheeky second kill!
Dakka Dakka Dakka? Psybolt ammunition is cheap but turns heavy bolters from being average, into being good, when paired with an assault cannon you're putting out a hail of bullets that people aren't going to like. Hurricane bolters can add to this effectively but here psybolts almost turn into a disadvantage as you end up without the bonus of them being defensive weapons.
The main drawback to using the stormraven in this capacity is that if you have many GK around you're unlikely to need more anti-infantry firepower... if you're tripping stormbolters you don't need to use up the gunship's hardpoints for more of the same.
Although much as I like having effective units, arguably one of the biggest advantages of this weapons set up is the fact you get to make machine guns noises with your aeroplane... I mean, how good is that?
Winning Hearts and Minds? The mindstrike missiles don't strike me as being that hot. Mildly improved frags with longer range... I guess you might as well fire them off should you get the chance, after all you've paid for them and there is no bonus for bringing them back unused.
Their anti-psyker ability is very limited usefulness, unless its an all psyker unit or you can cause enough wounds with them to force some hits to get allocated against the psykers you're probably not going to get to use this rule. That said, if you get your sights on a librarian in a small unit, it could be worth a go!
In summary the Stormraven clocks in largely as an alternative to land raiders, while technically it has more speed I doubt it'll frequently get units into combat quicker. Its both more and less resilient in different ways, but from first impressions is a good addition to the Grey Knight's motor pool.
I hope some of the ideas here help you with the gunship's use, I'd love to read other people's ideas, tricks and tactics. I may fold this into an article at some point to help flesh out the rather empty Inquisition section, so can I can assure that anyone contributing will be fully credited.