Deathstrike Missile Launcher
It's time. You need to give your foe the finger in defiance.
But not just an ordinary finger, oh no.
You want to go for a giant middle finger, one which will launch into the sky, then come crashing down and trigger an explosion of apocalyptic proportions. Well good news, Guard players: You have an option. This option happens to be the single most over-the-top thing in the Imperial Guard, and that's saying a lot for an army that fields tank battalions the size of small countries and batteries of artillery capable of raining death from across a table. You want to nuke the motherfuckers, and the Deathstrike Missile Launcher will allow you to do just that. It's time you brought in the frontline ICBM.
Overview
The Basilisk Artillery Gun and other artillery used by the guard have numbers.
The Manticore Rocket Launcher has its cluster-bomb effect.
The Deathstrike Missile Launcher has raw, balls-out power.
Put yourself in the mindset of the commanding officer:
"Gunner, do you see that army?"
"Yes, milord."
"I don't want to."
"Understood, milord."
And there's the reason to bring one in a nutshell.
The first thing to note about the Deathstrike is that it has only one shot, and takes at least one turn to be suitably prepped to fire - so it cannot fire first turn. It also cannot fire if it has moved. It has the rule "The Hour is Nigh," which means that you need to roll a d6 every turn after the first for the Deathstrike, adding +1 for each round the Deathstrike has been on the table and stationary, and subtracting -1 for each weapon destroyed result the missile has taken. If the result is 4 or greater (a roll of a natural 6 is an automatic success), the Deathstrike may fire its missile.
Why suffer all these penalties for a one-shot weapon? Why bother going through all this for a vehicle whose drawbacks are easily eclipsed by the upsides of the Basilisk, Colossus Siege Mortar, and Manticore Rocket Launcher? The answer lies in the Deathstrike's overwhelming power. That one missile has unlimited range, is Strength 10, AP1, ignores cover saves, auto-hits everything in the blast, and deals its full strength of 10 to any vehicle caught even remotely in the blast area. Topping it all off, its blast radius is 10", which will make blob armies cry.
The most subtly hilarious facet of the Deathstrike is its unlimited range. You can literally fire it at another continent.
In short: Anything in that blast radius that doesn't have Eternal Warrior just had to roll for Anal Circumference. It has a Heavy Bolter, too, but no one cares about that.
Tactics
Sadly, the Deathstrike's weaknesses of only one shot, long ready time, middling accuracy (actually now fixed to a fucktastic Apocalyptic Blast), and variable blast size makes it a bit too chonky to be used effectively in a typical game. It's extremely effective when it fires, and it can utterly invalidate almost any enemy unit it targets, but it pays a lot for this. Getting the most out of the Deathstrike usually involves fitting it with Camo Netting to make it stealth, and a Hunter-Killer Missile, optionally, to let it do something when not sitting around waiting for the gun to fire.
Or you could just use it as the ultimate freak-out unit, like a distraction carnifex your opponent will focus a lot of effort and energy into getting rid of it before it has a chance to fire. Use 30 of them in an apocalypse game for the ultimate lulz.
Another use in apocalypse is to take it as the Deathstrike Vortex Missile formation (giving it "fueled and ready for launch", which reduces the number you have to roll to launch the thing). This can then be used to snipe off annoying enemy characters (or titans, or gargantuan creatures) as an amazing display of overkill.
Alternatively, phone up a distant Games Workshop, and tell them that you're targeting your Deathstrike Missile Launcher across state lines, to attack a randomly chosen game going on at their store. Even the Age of Skubmar ones, or the maybe three remaining Hobbit games on the planet.
As a side note, We all know that cockroaches are immune to fallout so Tyranid's big monstrous creatures (f.ex those that you WANT TO KILL with this thing) can shrug off deathstrike missile's effects with Feel No Pain, Regeneration or just not giving a fuk with 5 more Wounds to go on. However, when against spehs mehreens, this is the ultimate troll machine for instakilling everything.
Thanks to unbound lists in 7th e, you can legally field an army consisting of nothing but 15 deathstrikes at 2k. That is how you man-mode 40k.
++Thought of the Day: Know your Enemy, Prepare Thy Anus.++
Vortex Missile
For even more rape you can take in a Deathstrike launcher armed with a Vortex Missile. This monster has the same blast but it would instagib ANYTHING, save gargantuan creatures, super-heavy vehicles (who lose D6 Wound or D3 SP respectively), and independent characters who have rules that come into play when they get removed from play like Trazyn or Saint Celestine. No saves of any kind, no eternal warrior, no rolls for damage, no reanimation protocols or other back from dead bullshit - everything under blast template would be just thrown into the warp. And the vortex blast would stick around as a 3" marker, scattering 2D6" at the start of both players turns with the same rules, only disappearing when a double is rolled. Taking one of these is a nice way to bring a game to a friendly conclusion
8th Edition
The "accessibility" nerfbat has arrived, and as one of the most fun units the IG have the Deathstrike was hit the hardest.
An ordinary Heavy Support choice for 163 points stock, and the missile is 3D6 shots that inflict a mortal wound with every hit, no wound rolls required. Sounds great, right? Unfortunately there are a few other things to consider. It lost its unlimited range - even if it's still 200 inches it's now out-ranged by a Basilisk, and the Inter-Store Ballistic Missile is gone because that would be too much fun. Most devastatingly, as a result of the removal of templates, it now only actually lands half of the missile's 3D6 hits because it has BS4+ (and that gets even worse if the launcher is damaged when it fires) and only hits a single unit directly - although it is, at least, one of the few weapons to retain some form of splash damage, with any unit within 6" of the target suffering D3 mortal wounds on a 4+ (whoopee). Not exactly the machine of terror it used to be, considering its average damage-on-target is just 5 wounds (3D6->10.5 hits, halved by BS4+) to a single unit in an edition where most large targets have at least 12 Wounds and access to an ability (or even several stacked) that will let them ignore those on a 5+/6+, and hordes come in squads of 30. You might get the odd one that obliterates a tank or Terminator squad if you roll well, but generally these will now just kill a few Meganobz or scuff the paint on a Land Raider, and they actually have the real potential to miss altogether (don't question how one misses with a megabomb). Unless you spend a lot more points to stack a shedload of to-hit buffs and rerolls on it, it's unlikely to achieve more than mildly annoying a couple of squads. But there will be that one game where it will hit with all the shots. Just for witnessing that glory, it is worth it.
9th Edition
Welp, explosive weapons will now deal max hits to hordes.
See Also
A fourth of July celebration in which a nuclear war is started between Britain and the USA, fought with Deathstrikes.
GW's Vortex Missile datasheet