Skyray Missile Gunship
Oh, the Skyray.
Sweet, beautiful, underappreciated Skyray.
It will never be as common as the Hammerhead, or Broadside Battlesuit teams, nor will it ever be as celebrated, and yet it remains there, acting as the favorite Heavy Support choice of Ninja and Infiltration Tau strategies everywhere. Notable mostly for the rather unique (and useful, dammit!) rules behind its main weapon, a battery of 6 seeker missiles, it is a fairly versatile weapon platform. Unfortunately, it's pricey, and takes up the oh-so-essential heavy support choice slot in a given Tau Army—which, unless the army in question is either heavily focused on mobility or has more than the usual ass-load of markerlights in it, generally isn't a nice thing.
Still, it's a fun vehicle and genuinely useful if used correctly, so it gets a nod here.
Tabletop
The Skyray itself is a gunship—a classification the Tau have also given to the Hammerhead, since it's designed to be a support unit. It boasts surprisingly heavy armor (for a Tau vehicle), and has the natural ability of Tau vehicles to pack on a field and get a cover save. What truly sets it apart from other vehicles, however, is that its main weapon—seeker missiles—don't quite work like any other weapon in 40k.
Fans of the Imperial Guard have a love-hate relationship with the Hunter-Killer Missile. Whilst it can give a vehicle first-strike punch due to its unlimited range, it usually costs too much and is too wonky to be considered a serious anti-vehicle option. The Skyray gets around this problem by means of simply being a carrier for a large number of the Tau's nifty-swell precision-guided missiles—and is noteworthy in that it is not the source of its own missile attacks (usually).
See, when Tau Pathfinders or the like markerlight something, the markerlight counters are normally spendable on improving a unit's BS, or reducing an enemy's cover save. If you have a Skyray, you can spend a point launching one of the Skyray's seeker missiles at it. These missiles not only boast unlimited range as well as firepower equal to a Hunter-Killer missile, but they don't even need line of sight to drop a missile strike. In other words, the Skyray can provide long-range support and provide multiple simultaneous and devastating defensive missile strikes as long as it has markerlight support. It's particularly effective at butt-fucking Tyranid monstrous creatures and light or medium armor that thought it had a helpless unit for prey, not realizing that the squad could call in a cruise missile from the Skyray.
In a pinch, the Skyray has 2 markerlights of its own—and yes, it can lock and fire its own missiles in said pinch. If that's not enough, it also can pack burst cannons, drones, or a smart missile system (the latter being widely acknowledged as the better option) to deal with infantry units or heavy infantry, respectively S5, AP5 won't really cut it against heavy infantry. With its solid armor, the Skyray won't usually suffer for the change of pace, since no matter what action it takes—shooting its main weapons, dropping markerlights, or even parked in your deployment zone acting as a fuck-bus for a very bored Shas'ui—it's going to get shit done, /tg/ style. And most likely, not during its own firing phase.
If all else fails, the Skyray can stand still for a turn, fire off its networked markerlights, then fire its seeker missiles as regular weapons; using this you can launch up to six missiles at BS6 instead of two missiles with Ignores Cover. Say goodbye to that Command Squad or group of Berserkers.
But Then, Hammerheads
"But wait!" yells the concerned non-Tau player, perplexed by this article, "This unit sounds awesome. Why isn't it used that much?"
The answer is simple: Railguns.
The Tau Hammerhead Gunship and Broadside Battlesuit are both heavy support choices, both have AP1 Railguns (the Hammerhead with S10 and one shot or a Broadsides squad with S8 and three shots,) and Railguns will never disappoint as an antivehicle option - whereas the Skyray's missiles are S8 AP3 - great for busting open enemy Crisis Suits (lol) and the errant Carnifex, but horrible against the big scary AV14 Armor that tends to hit the table when fighting Space Marines, Chaos Space Marines, or the Imperial Guard. The Skyray's deficiencies are especially notable on more conventional Tau army lists; whereas one can take a Hammerhead on virtually any mission without becoming a liability, a Skyray can be mighty difficult to justify when its lowered performance against Predator Tanks and Leman Russ Battle Tanks causes glancing hits as opposed to penetrating ones (though the Skyray is just as durable as more conventional tanks, if not more so).
Even though the Skyray can provide multiple support strikes in the same turn, it's simply just not as good as other choices. Heck, even the Hammerhead can double as an anti-infantry weapon too, since it has submunition rounds that also ignore cover and cover a wider area. No matter how boss the Skyray is (and it's very, very good), it will never be able to hold a candle to the undiluted armor-rape that are Broadside/Hammerhead Railguns. On top of that, the Skyray isn't even that much cheaper than other options; even if it were considerably cheaper, it still wouldn't really justify taking up precious heavy support slots.
Even if a player really wants to include seeker missiles, the Skyray does not own a monopoly on them. Though it brings more of them to the table than any other one source, many other kinds of Tau vehicles can mount a pair of seeker missiles each, including the Devilfish, Piranhas, Razorsharks, and hell, even Hammerheads can mount a couple or Broadsides can mount one each, giving you railguns and seeker missiles in the same package and without taking up extra unit slots. The Skyray is certainly helpful in getting them, but by no means critical.
Also there's the fact that it used to cost more base than a hammerhead, only had 6 shots (that could be fired all in one turn for some douchey and hilarious extermination of that precious little Carnifex over there) and thus become a floating, overpriced Smart Missile System, and of course in 5th edition's focus on mechanized play players would do better to take the seeker missiles on all their vehicles, thus spreading them out and reducing the chances of a single shot taking out all your HK knock offs. The weakening of vehicles in 6th has not been kind to it either, especially now with the emphasis on fliers and the Broadside's superior ability to take them on (since you can get a broadside with skyfire for 20 points less at minimum that can fire the same number of shots over the course of a game and isn't beholden to the luck of your markerlight rolls, or for 50 points more than a bog standard skyray you can get two broadsides with skyfire and the ability to spit out twice as many shots as a skyray over the course of a game)
However...
On the other hand, the Skyray does have a few uses on the battlefield. It works very well with mechanized Tau and Battlesuit-heavy lists (esp. Ninja Tau), since these are less likely to have oh-so-precious Markerlights, and a number of Tau Armies field one to back up their Broadsides and/or Hammerhead - since it's kind of hard to argue that Seeker Missiles aren't fun as hell to use. Armies which use fucktons of Markerlights frequently have several, since one critical advantage the Skyray has over the Hammerhead is that it can fire numerous times in one turn if the Markerlights allow for it. Another key advantage is that again, Skyray missiles ignore line of sight restrictions and terrain obstacles when fired at their target - this makes Skyrays far more useful in urban combat scenarios, since they'll never have to shoot through terrain obstacles to get at their targets. The Skyray also has a velocity tracker alowing it to have two skyfire markerlights, turning it into a formidablr anti-flyer weapon.
The point is that Skyray Missile Gunships have their uses, provided you consider their strengths correctly. They may not have the raw firepower of Hammerhead Gunships or Broadside Suits, but the ability to drop extra markerlights or provide highly accurate indirect fire support anywhere a markerlight is drawn can be quite useful under some circumstances.
And then 7E
With the removal of requiring armies to follow the Force Organization Chart, nothing is stopping you from saying "fuck the formation bonuses" and picking up one of these in addition to your other heavy support options.
The wisdom of doing this, though…is completely solid! After alpha striking with 6 missiles on turn 1, and disembarking their drones, Skyrays form assault shields with markerlights that are hardly worth the opponent's trouble to kill. There's also, of course, the possibility of loading up on all the Skyrays you can get your hands on and making a list with them, so you can FIRE ZE MISSILES turn one for an absolutely hilarious game for both sides.