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 Tanks 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.
Overview
The Basilisk 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.
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 "T-Minus Five Minutes... And Counting," 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 subtracting -1 for each weapon destroyed, crew stunned, and crew shaken result the vehicle has taken. If the result is 6 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 960" 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 variable - 4-6 inches (d3+3) - making it capable of the biggest explosions of any artillery vehicle. For contrast, a blast template is 1.5 inches in diameter and an ordnance blast template is 2.5 inches in diameter. The Deathstrike's blast can be up to six!
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 it.
Tactics
Sadly, the Deathstrike's weakness is its combination of only one shot, long ready time, middling accuracy, and variable blast size. 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.