Capabilities - I feel the key to understanding where and when to apply a unit in any given situation is informed by knowing their full capabilities off by heart; here is a look at what this unit is capable of.
There's normally a lot to discuss with most monstrous creatures, but I feel the Ghostkeel might rank chief among them for rules figuratively stacking atop each other. Let us begin with the basics; for one, it is close to owning the bottom of the barrel in terms of melee capabilities for a model of its unit type. Weapon Skill 2 is abysmal and ensures almost any opponent will hit a Ghostkeel on a 3+ in close combat, while the Ghostkeels themselves will instead hit Weapon Skill 5 or higher opponents on a 5+. Three base Attacks isn't too bad, especially when they are at a high Strength 6, but that crippling Weapon Skill 2 and even more painful Initiative 2 put the Ghostkeel at a significant disadvantage against even the most bare bones of assault forces. Having Smash does mean that all of those attacks are at AP2 and as such the Ghostkeel can still rely on the crutch of its unit type to beat down lesser foes, while Toughness 5 enemies or vehicles can be felled via the optional single Strength 10 AP2 attack that re-rolls failed armor penetration rolls. It can theoretically harm anything in the game and still has the defensive stats to survive and further overwhelm basic infantry units such as Tactical Marines, especially if you account for the singular Strength 3 AP- attacks offered by each of its two accompanying Stealth Drones that are Weapon Skill 2 and Initiative 4. However, the mandatory nature of those Drones and the lack of Fearless does mean that Ghostkeels are particularly susceptible to fleeing; the Drones do share the same Toughness of the Ghostkeel but only have one wound each with a 4+ armor save for defense. Smart opponents can simply focus down the Stealth Drones and force Morale tests on the parent Ghostkeel, while it is especially vulnerable to this in close combat given the fact that it can actually be caught by a Sweeping Advance. In any case, that the Ghostkeel causes Fear does give it a slight edge in close combat against a select few armies; every advantage helps in such circumstances.
The Ghostkeel is fairly mobile as far as monstrous creatures are concerned given its Jet Pack classification, the full uses of which are based on avoiding direct confrontations with potent short-ranged attackers. It can freely choose to ignore intervening terrain when it moves up to 6" in the Movement phase at the risk of destroying its own Stealth Drones, both of which also use Jet Packs but are vulnerable to Dangerous Terrain - the Ghostkeel is not susceptible to Dangerous Terrain as it has Move Through Cover. However, it is important to note that all the other benefits of Move Through Cover are spread to the entire squad and thus the unit can more safely roll 3D6 choosing the highest to clamber across terrain, and does not suffer from reduced charge ranges. It can also, in lieu of charging, elect to move 2D6" in any direction during the Assault phase with the same possibly self-destructive results for the Drones as in the Movement phase. This allows you to play out the same jump-shoot-jump scenario that Crisis Teams popularized all the way back in the original Tau codex, albeit this time with an over-sized cloaked predator that can be even more vicious in larger unit sizes. Of course, it isn't quite so simple to capitalize on as it is for Crisis Teams or Stealth Teams; a Ghostkeel is a fairly large model and thus hiding it will often not be possible whatsoever, but mainly you just want to use the Thrust move to keep out of charge range without compromising on damage output. Also, don't underestimate a Ghostkeel's ability to zip across the battlefield and secure an objective or other positional-oriented victory point; moving an unobstructed 6", D6" and 2D6" in the Movement, Shooting and Assault phases respectively thanks to Running is a lot of coverage for a model that many units will still want to avoid in a melee.
At range, the Ghostkeel is a solid competitor that isn't quite on the same level of raw efficiency or power as a Riptide but nonetheless will still be a not inconsiderable threat even to the toughest of foes - what else would you expect of a Tau battle-suit? It is always armed with two distinct weapons, one primary and one secondary; these can range from Wych-dicing Burst Cannons to Terminator-obliterating Fusion Colliders. A Ballistic Skill value of three is expected of a Tau model but still irritating in the sense that it really forces you to employ Markerlights or other accuracy-boosting tactics to get full value out of what is, all things considered, not exactly a cheap unit. One such way to get around the deficiency is to field Ghostkeels in squads of three (or nine if you include the Drones) thanks to the Fire Team special rule, a much appreciated addition to the new codex both for existing staples and the all-new XV95's. Formations such as the Optimized Stealth Cadre and Ghostkeel Wing also offer similar benefits, but your primary method of doubling down on the strong guns that these battle-suits wield is still undeniably Markerlight tokens. Three are the bare minimum required to really unlock the full potential of the Tau armies' heavy weaponry with a slight bump to the Ballistic Skill of the user and that incredibly powerful Ignores Cover that distinguishes Tau from nearly all other factions, with four tokens being unnecessary should Fire Team be in effect as well. Of particular note about these weapons is that they are best suited to hunting medium to low Toughness units and light vehicles - in the case of the Ion Raker and Burst Cannon - or disgorging pure devastation upon well armored targets of both the organic and vehicular types - courtesy of the Fusion Collider and Fusion Blaster. What each of them shares is a medium to short range, normally 18", that forces the Ghostkeel to stay in close proximity to their targets, hence the reliance on the Thrust move detailed above. It results in an interesting paradigm of risk versus reward that most Tau units normally don't care for, especially if you want to gain the advantages of the Melta special rule offered by the two distinct Fusion weapons. Sadly, the Stealth Drones attached to each Ghostkeel do not offer any kind of firepower of their own.
Of course, what those aforementioned MV5 Stealth Drones are useful for is providing ablative wounds to the Ghostkeel and amplifying its stealth capabilities. Both they and their controller are Toughness 5 with the Drones having one wound apiece and a 4+ armor save, whereas the Ghostkeel has four wounds and a 3+ armor save and possibly on top of optional (albeit costly) 4+ invulnerable saves and 5+ Feel No Pain rolls. The lack of an in-built invulnerable save, no 2+ armor save and a medium Toughness value of five ensure the Ghostkeel lacks the durability of a Riptide at first glance; of course, the devil truly is in the details here and this may take a little while to explain. The Ghostkeel itself has the Stealth special rule which then confers onto its Stealth Drones, giving them a 6+ cover save. The MV5 Drones possess a Stealth Field that, because the unit already has the Stealth special rule, instead confers Shrouded on the unit to give them +2 to their cover save for a cumulative 4+ cover save. This permanent cover save stacks with other sources of cover such as terrain or obscured firing lanes to easily give them a 2+ cover save. Next, the XV95 itself is outfitted with a Ghostkeel Electrowarfare Suite; if an enemy unit targets the Ghostkeel squad and is more than 12" away when firing, the Ghostkeel squad doubles the cover save bonuses offered by both Stealth and Shrouded. This means that Ghostkeels and their Stealth Drones permanently have a 2+ cover save even in the open unless the unit attacking them is within 12", though as discussed extensively the Ghostkeels are more than capable of playing keep away against slower foes. Basically, as most heavy weaponry that would bypass all armor saves tend not to also have Ignores Cover, a Ghostkeel is actually more durable against most shooting attacks than a Riptide with few exceptions. Strength 10 guns are always nasty due to the potential Instant Death that Riptides need not worry about, while the higher Toughness and 2+ save of the larger battle-suit give it the edge against small arms fire. However, as most methods of dealing with monstrous creatures involve Graviton or Plasma weaponry, the Ghostkeel stands tall against the incredibly hard hitting ranged units that have characterized both 6th and 7th Edition so far.
In the rare case that enemy attacks do bypass a Ghostkeels' already considerable defenses, it is outfitted with one final barrier; manifesting as Holophoton Countermeasures, this functions by overloading the weapons of would-be aggressors and momentarily rendering them all but useless. They can be activated in any opposing Shooting phase with a one-use-only restriction; the moment any enemy unit targets the Ghostkeels (meaning they cannot switch targets), you can choose to activate its Holophoton Countermeasures and force all of their ranged attacks to Snap Fire for that phase regardless of whether all of the weapons in the unit fire at the XV95's. This works on any unit, even mighty Super Heavy Vehicles, and as such normally gives Ghostkeels one full turn of safety at a moments notice given that the weapons capable of truly harming them will usually be few and far between in most army lists. Take a competitive Space Marine army centered around a large Centurion Devastator squad for example; the main source of Ignores Cover will manifest in any psykers attached to that unit, meaning that you can save the Holophoton Countermeasures for them should they dare to fire at the Ghostkeels. This will often act as a deterrent to players as they can be unwilling to fire at something they know could potentially soak up several hundred points worth of shooting unscathed, but generally speaking it means that Ghostkeels are far better fire magnets than Riptides in terms of actually surviving the incoming punishment. Of course, this rule isn't without some controversy; the wording of how it functions when multiple Ghostkeels are present in a single squad is rather confusing, but the generally agreed interpretation is that Holophoton Countermeasures can be activated as many times as there are Ghostkeels in a unit. With all that said, what the Ghostkeels are built for becomes rather clear; they are a forward roving Riptide alternative that can actually survive all that typically medium to short ranged shooting with the Graviton, Plasma and Melta types, but it does this by sacrificing raw firepower and durability against most small arms fire.
How to Equip Them - Outfitting a unit is often even more difficult than determining the number that you employ, so having appropriate context for each choice is key; this rounds out the most optimal ways to equip a squad.
Ghostkeels are in the appreciable position of having to choose between multiple mostly equally valid options for both their primary and secondary weapon systems, with a wide range of different circumstances providing unique answers to the question of what gun reigns supreme. First up, you get to freely select either the Cyclic Ion Raker or the Fusion Collider as your main damage dealer on the Ghostkeel, the former offering either six Strength 7 AP4 shots or one Strength 8 AP4 Large Blast - both at 24" - and the latter firing one Strength 8 AP1 small blast at 18" with the Melta special rule. These weapons do have inherent risks to their utilization through their medium to short range or the fact that the blast profile of the Ion Raker features Gets Hot, and while the potential overheating isn't much to worry about for a four wound monstrous creature, any kind of low range is normally frowned upon for Tau. Ghostkeels do mostly skirt this issue but the fact that there is a 6" gap between the Ion Raker and the Collider, plus the consideration that the Collider only benefits from the Melta rule within 9" of the target, the "safer" option is undeniably the Cyclic Ion Raker. It is also the more universal as it has incredible rate of fire on a high Strength weapon making it a great weapon to combine with a Velocity Tracker or to generally bring great harm to a wide range of targets, while that large blast profile also does light to medium infantry hunting better than the Fusion Collider. However, should you be taking the Ghostkeel in place of Riptides that are the standard source of AP2 blast weaponry in a Tau force, the Fusion Collider becomes the more appropriate option given that you can potentially combine Markerlights for Ignores Cover with an incredibly strong AP1 small blast at close ranges - it also becomes a devilish tank hunter in such a scenario. For the most part, I give the slight nod to the Cyclic Ion Raker for its increased range and versatility, while it is also generally the best weapon to use if the Ghostkeels are party to an Optimized Stealth Cadre; the lower Strength and lack of Melta are unnecessary when striking the rear armor of vehicles wherein the higher rate of fire of the Ion Raker reigns supreme.
On the flip side, a Ghostkeel has a larger selection of tools to choose from in its secondary weapon slot, all of which are twin-linked; a flamer, a burst cannon and a fusion blaster. The first is free and the third is more expensive than the second by a handful of points, and I will immediately clarify something else; ignore the flamer completely as its range is just far too small and the Ghostkeel still mostly anemic to close combat for it to be worthwhile for anything other than skirting points limits. With that aside, the Burst Cannon and Fusion Blaster both have their own merits; the former is cheaper and fires four Strength 5 AP5 shots at 18", while the latter is at a slight price disadvantage but piles on the pain with a single Strength 8 AP1 shot also resolved at 18". Most prefer the Fusion Blaster for the extra anti-tank shot that is also equally capable of pinging off a Terminator equivalent or wounding a monstrous creature, neither of which can really be emulated by the Burst Cannon. The difference between Strength 5 and Strength 8 is far more significant than with the Strength 7 and Strength 8 for the primary weapon systems, meaning the Fusion Blaster better supplements either the Ion Raker or Fusion Collider for the targets that Ghostkeels tend to focus on. Of course I do like the Burst Cannon as well as, especially in an Optimized Stealth Cadre, a plethora of Strength 5 shots striking the rear armor of vehicles is still nothing to sneeze at and the rate of fire allows you to force through saves on nearly anything; just don't expect the same kind of results as you probably would from a Fusion Blaster that also benefits much more from Ignores Cover. Moving onto the other various equipment selections you can outfit your Ghostkeels with, the Bonding Knife Ritual is a nice and cheap option for the unit given numerous factors. You need only pay for it on the battlesuits themselves, their mandatory Stealth Drones greatly increase the chances of Heroic Morale coming into play and that handful of points can mean the difference between a large and expensive unit fleeing the field or staying true to the Tau doctrines and assisting your victory.
A wide range of Support Systems are open to Ghostkeels of which it can purchase up to two on a per model basis, though one in particular is annoyingly barred to them; Vectored Retro Thrusters would be a perfect addition to what is ultimately an oversized medium to close ranged stealth support unit, though I understand from both narrative and balance perspectives why it is unavailable here. A couple of the other upgrades are either effectively useless or not worth it for Ghostkeels - Drone Controllers don't function as Stealth Drones don't have weapons, Positional Relays are better left to your actual Infiltrators or Deep Strikers, and Counterfire Defence Systems don't help Fusion Collider-armed Ghostkeels and ultimately are a last ditch effort to combat poor positioning on your part for letting Ghostkeels get charged. Both Stimulant Injectors and Shield Generators are massively expensive for XV95's and are only really useful in close combat (where it doesn't want to be) as a near permanent 2+ cover save and Holophoton Countermeasures make it all but impervious to ranged damage; if you face rare Strength 10 Ignores Cover weaponry or rapid assault forces then the Shield Generators become somewhat worthwhile, while the Stimulant Injectors are better in other situations. Advanced Targeting Systems provide the Ghostkeels with Precision Shots which can be utterly lethal with their high rate of fire weapons and various damage-boosting buffs from outside sources, or useless should you use blast-type attacks. Early Warning Overrides combined with either the Ion Raker or Fusion Collider for an imprecise but deadly unit-killing shot are ideal against clumped up squads arriving from Deep Strike. Combining Interceptor with optional Skyfire from a Velocity Tracker can give most flyers a scare should the Ion Raker be your weapon of choice, though should an Optimized Stealth Cadre be in play then waiting to benefit from the Wall of Mirrors can reduce the need or want of Early Warning Overrides. In all actuality, Ghostkeels bearing Cyclic Ion Rakers are superior to Riptides outfitted with Ion Accelerators for anti-air duties, so Velocity Trackers should definitely be on your prospective to-buy list. Target Locks are ideal for squads of two or more Ghostkeels to optionally allow you to split their considerable firepower between multiple units; just be sure not to make the rookie mistake of giving all members the upgrade as one will never need it due to firing at the primary target. Ultimately, I think keeping Ghostkeels cheap - unless you take a large unit of them or utilize the Optimized Stealth Cadre - is ideal as they do have major vulnerabilities that well equipped opponents can exploit regardless of how you outfit them, meaning they aren't quite so easy to just slot into an army with high expectations like a Riptide.
Best Uses - It is true that each unit in the game ultimately has one or a handful of tasks they are best suited for in a general sense; these are the most efficient uses of this unit based on their capabilities.
A quick summary for this section would likely read "optimization of Ghostkeel units is dependent on what type of detachment they are a part of" and for good reason; the Tau Empire has an incredible wealth of formations and composite detachments to choose from, each with their own unique advantages and disadvantages for the XV95 battlesuit teams. In a Combined Arms detachment, the Ghostkeels are entirely reliant on Markerlights to boost their damage output and necessitate between three (if Fire Team is in effect) and four to enjoy the lovely mixture of Ballistic Skill 5 and Ignores Cover. In that case, you want to use Ghostkeels either to supplement your Riptides as more efficient anti-air platforms or, if you replace them, to be a forward roving alternative that is much more resistant to shooting but both less of a damage-dealer, and not a tank in close combat. In a Heavy Retribution Cadre, you need only one Ghostkeel to act as the supporting cast for the pair of Stormsurges; opponents are more likely to focus on harming the Stormsurges that are far from impervious to damage rather than the irritating Ghostkeel, powerful as its special buff might be. In an Optimized Stealth Cadre that is not privy to the Hunter Contingent benefits, a full team of three wielding Target Locks (one less than the number of Ghostkeels in the unit) maximizes all of the special bonuses both the formation and Fire Team rules provide - however, keep in mind that the larger the unit is, the more vulnerable it becomes to assaults and morale-affecting shenanigans.
On the flip side, you need not consider an Optimized Stealth Cadre should you make use of the Hunter Contingent depending on how you play the Combined Fire rules; regardless of whether you believe special rules are shared between constituents of the detachment, sharing Markerlight tokens gives you most of what you would otherwise purchase an Optimized Stealth Cadre for. Of course, that particular formation gains the ability to shoot at the rear armor facing of vehicles regardless of individual model placement and it has no need of Markerlights should you employ it, meaning you can have it operate individually and leave the Combined Fire to the rest of your forces. The same basic rules apply in a Dawn Blade contingent, albeit with less degradation of the value of the Optimized Stealth Cadre. In either of those detachments, the Ghostkeels function as they do in a Combined Arms detachment; a replacement for Riptides with its own ups and downs as to why you should use it, or as a small addition to an army. I tend not to like full-sized units of XV95's outside of the Optimized Stealth Cadre given the amount of points in both the unit and supporting elements - namely Markerlight sources - required to really maximize their destructive potential, something that they ultimately can't really match Riptides for in most circumstances. The Ghostkeel Wing is an interesting formation with lower minimum requirements than the Optimized Stealth Cadre, trading weaker buffs for the Ghostkeels themselves to instead give them the role of defensive amplifiers to the rest of an army. Providing either minor or major cover bonuses to other Tau units greatly improves their core issue of durability for anything that isn't a monstrous-sized or vehicular model, dramatically increasing the effectiveness of Tau infantry.
In all cases, regardless of which type of detachment you choose to field your Ghostkeels in, the unit tends to fill some familiar archetypes to veteran Tau players; namely, it is an odd hybrid of a Riptide and a Stealth Team. It has lower damage output in identical points limits to Riptides and Crisis Teams but is superior to Stealth Teams in that aspect, it is more difficult to kill overall than any of those units barring Riptides, but it is by far the most resilient Tau model in the codex against shooting attacks - Graviton is a nightmare for Riptides and, to an admittedly far lesser extent, Stormsurges - but it may as well be worthless against a Ghostkeel. The fact that all of its guns are 24" (just one) or less (the rest) means that positioning is more important for it than most other Tau models, particularly the Riptide it competes for a slot against. You can't just have it sit back and pepper opponents from afar, especially as its guns don't really have the damage output to work in the same manner as a Riptide would. Obviously, this means it is intended to be used as a close-ranged fire magnet that tries to draw heavy attention away from the rest of your force given that it's near permanent 2+ cover save and one-use-only pseudo-Invisibility ensure opponents need to dedicate incredible amounts of firepower to even scratch the Ghostkeels' armor plating. Unless you are in close proximity to opponents, you need not worry about using terrain to get the full 2+ cover save; it is dangerous to use as it can potentially destroy the accompanying Stealth Drones and thus eliminate a major defensive addition to the XV95's repertoire. Making liberal use of its Jet Pack movements in both the Movement and Assault phases is required to keep it out of combat or nastier close ranged shooters (there's no reason not to reduce potential incoming damage regardless of how unlikely it is to harm the target) while allowing it to stay in range of enemy units. Charging it into close combat isn't a terrible idea in many circumstances as it is still a monstrous creature with four Strength 6 AP2 attacks on the charge, though unlike a Riptide it lacks the armor save and Toughness to resist incoming damage, while the forced use of Stealth Drones gives opponents much easier methods of harming the units' morale.
Lastly, keeping its Holophoton Countermeasures in reserve until you face a shooting attack that will truly harm the Ghostkeel is key to keeping it alive for as long as possible; Ignores Cover can be spread to many different units through psychic powers or opposing Markerlights, so making sure to identify what is most likely to harm the XV95's in the enemy forces is a necessity. Destroyer weapons are a common choice to activate your Countermeasures against, as are attacks such as those offered by a three-strong Vindicator squadron, Typhon Heavy Siege Tank or others that bypass both the Ghostkeels' cover and armor saves while additionally inflicting Instant Death. Be sure to enforce the FAQ ruling that Gargantuan Creatures and Super Heavy Vehicles must declare all of their targets before firing any of their individual weapons, as the moment they pick a Ghostkeel as one of those targets you can activate its Holophoton Countermeasures and force all of the weapons on the leviathan in question to fire Snap Shots. If you field the Ghostkeels in a squad and play with the widely accepted ruling that you can activate the Holophoton Countermeasures once per Ghostkeel, you can afford to be more liberal with them as you can guarantee between one and three different units (or the same unit across multiple turns) is rendered nigh useless against your pricey monstrous creatures. Be mindful that you do want to use this incredible defensive tool at some point in a match and not just leave them unused, because you can certainly avoid a lot of trouble by simply activating them at an inopportune time; if you feel the Ghostkeels are about to be charged, staving off any potential wounds in the preceding Shooting phase is worth burning the Countermeasures on. The trick is always to familiarize yourself with what weapons are present in an army, evaluate which is most likely to harm your Ghostkeels and whether secondary rules from outside sources can change the equation for any given gun selection. Markerlights and, consequently, other Tau armies, are a tough nut for Ghostkeels in one sense that massed hits can quickly expend the Holophoton Countermeasures, while stray shots from Stormsurges are more than capable of obliterating a unit through unlucky dice rolls. However, the Ghostkeels do have the advantage of not being scared of combat (for the most part) against a Tau army and are thus more free to rapidly close with enemy battle-lines where their weaponry can make short work of most Markerlight sources.
Thank you all for reading this article, I hope you enjoyed it! Ghostkeels are a good unit on their own merits that act as a more durable alternative to the Riptide in the fire magnet role against armies that are reliant on shooting to win the day, though it does sacrifice raw damage output as a trade-off. Its close-ranged nature means that it is more difficult to effectively utilize than a Riptide given the greater focus on positioning; even so, it is an impressive choice to expand any Tau force and is utterly terrifying as part of an Optimized Stealth Cadre.
Forward, for the Greater Good!
- Aun'va, Ethereal Supreme of the Tau Empire