we are going to be running a ground assult on a planet. the enemy navy has met us in space and lost. we are going to have to make an opposed landing on the planet. to soften up the defenders we are planning to use one of our atomics to airburst over the main opposition base to cause the normal damage + hit their armor and air assets with a emp blast. Our gm is having a bit of trouble working out the effects of this. any ideas? naturally the blast is going to cause blast and radiation damage to the infentry, and anything in the air is screwed. but what about air and armor units on the ground. any units that are in protected areas or bunkers? centeral command is under a void shield but what happens to the vox systems outside of the shield? thanks for any ideas.

40k technology in general and Imperial technology in particular tends to be pretty robust. Even today there is hardened military gear so it's entirely appropriate that the Imperial Guard equupment will have at least some protection from EMP. Bear in mind that nukes are regarded as outdated and inferior weaponry in 40k. Plasma torpedos and explosives are more destructive and don't leave as much hazardous radiation. That said, I imagine that whether the vox systems are fried or not (I guess not), they won't be usable since the local atmosphere will be full of interference.

Actually, given that it's canon (at least in the novels) that ordinary massed artillery fire will effectively jam Imperial Guard vox units through electromagnetic interference (don't ask me how that works), they can't be that well made. And nukes aren't outdated, as such, as frowned upon as being unneccesarily damaging to the environment, when it would be much cheaper to throw a million Imperial Guardsmen into the meat-grinder instead.

Of course, if you DO want to destroy the environment, cyclonic missiles and planet-crackers are the way to go.

I'd put an EMP blast effect, if it was deliberately set off high enough to cause such an effect, as disabling vox units until your tech-priest passes a difficult tech-use test to replace all the fried circuitry. Unless you're using vox-units inherent in void suits or other armoured gear, in which case they're unaffected.

There's a difference between jamming and shorting out voxes so it's entirely possible you can jam a particular vox all day long without it actually suffering electronic failure. That said, fair point on the atomics.

This could sound cheesy, but maybe go with Damage + Radiation + Haywire area. You might just say that most of the tech in the area of the blast, unless it is legitimately shielded (GM's call), suffers from the Haywire trait (in Deathwatch). That way, stuff stops working, for a while, but slowly reboots, and you might be able to use it, yourself, later. It would reflect the robustness of Imperial tech (ours would fry, and probably need various parts replaced), but it isn't over the top, and would seem to be a fair option. The effect is described as an electromagnetic disruption, so it even fits.

the haywire sounds like a good idea. another thing we came up with is auspecs are destroyed if they are outside a protected area. thick armor and shielding can't protect something outside it. so anything that would be on the outside of a starship would be on the outside of a tank so atleast part of it gets trashed.

thanks for the advice on the voxs.

Here's the thing so many people seem to forget when coming up with plans like this, if it were that effective of an approach someone would have done it already. Personally I would presume that given 40 tech seems to contain little to no micoprocessors (somehow) it would be almost entirely unaffected. Heck any aircraft capable of functioning in the void faces worse stuff then the ionic affects of an airburst. Yes coms will be somewhat screwed but to be honest so will yours.

Ah heres where having a dad that works as an electronics tech and being given NBC training in military pays off..lol....The actual effects of an airburst nuke EMP are simple...( if you want real )

ALL unshielded electronics in the blast radius ( not ground zero ) are flash fried..NOT repairable..they are toast....TOTAL overload and shorting out/melted down..this includes ALL electronics of all types including vehicles...whether powered on or off at the time..if they are not specifically shielded from EMP..then ALL their electronics are toasted ( requiring replacement ).....

ANYthing/one caught in blast that isnt heavily armoured will be likewise flash fried due to the ambient air temp reaching in excess of 3000* in less than a half second...THEN ...THEN you have the airwake/shockwave blast radius...extending out for however far the GM decides ( usually at LEAST a mile for even a small nuke ) that has intensely hot ( 500*+ ) radioactive winds blowing in excess of 300mph..

If detonated overhead then you will have a spherical blast zone for ground zero....ALL buildings above ground and not specifically hardened to withstand the extreme temps and heavy winds/shockwave WILL be flattened/obliterated and NO power armour is useless against an atomic blast IF your caught in ground zero area..and highly likely to be of only minimal protection if in immediate blast zone....most likely to become fused into whatever position you were in when the blastwave and intense heat hit you..and definitely short out ( only exception would potentially be perhaps a heavily shielded and armoured radiation suit designed for it )

Potential issues arising later from the blast are easy...

VEHICLES- tires are slag....treads potentially as well...turrets are sluggish to respond if not outright melted into current position...barrels will ALL be warped to one degree or another ( higher jam rate or even automatic detonation inside barrel upon firing )....

AIR UNITS- ailerons are melted into position...planes uncontrollable due to fins and ailerons melted into position/inopperable...canopy unlikely to be able to be opened or closed ( if open ) when blast hit

WATER UNITS- dead in water..total engine failure ( potentially catastrophic ) turrets etc same as vehicles above

VOX/COMMUNICATIONS- hope your in shouting range..because thats ALL your gonna be able to do for communicating distance...ALL voxcasting equip of all sizes caught in the blast radius is toast...period...and any going into area afterwards will be effectively jammed due to radiation flux within the zone until such time as the wind can disperse it .

Hope this helps.

That description of nuke effects, while accurate, only deals with ground level initiation and (relatively) low-altitude air-burst initiation of a nuclear device. High-altitude initiation (i.e. mesospheric, stratospheric or ionospheric in altitude, as opposed to low tropospheric), all that reaches the effected area is a quick gamma-ray burst, followed very shortly by an EMP (ok, and possibly some fallout much later, depending on device composition and wind direction). The EMP is generated by gamma-ray interactions with air molecules (a terrible term, air is a mixture of multiple gaseous compounds, each with it's own molecule, but that's a different rant) to produce Compton electrons. These then interact with the planet's magnetic field to produce a broad-spectrum electromagnetic pulse (<1Hz - 1GHz in frequency), which propagates in a mostly spherical manner (it can be deflected by the Van Allen belts, and presumably other strong EM fields) to fry those electrical systems within range and line-of-sight (ie, not behind sufficient shielding material). Obviously, as it is an expanding sphere, the EMP strength lessens with the square of distance from the point of initiation, but for a sufficiently large initial energy this does not in any practical sense limit range.

For reference, real world nuclear tests showed that a 1.4 megatonne device initiated at an altitude of 400km induced ground level effects 1300km away, while smaller yields only showed effects in an airborne intrument craft 300km away (although these could have been the result of SGEMP, the direct interaction of gamma rays with metals and particularly the wires of the electrical systems aboard, as opposed to Compton effect HEMP).

I will also note, that unless we speak of ground-burst or air-burst areas of effect (in which case, as has been pointed out, there are far worse things to worry about), that hardening a system against EMP, if considered in the design phase as opposed to a retrofit, can be done rather cheaply- a 1997 report to US Congress from the Defense Special Weapons Agency of the DoD estimated that it could be done for 1-5% of the cost of the system being hardened.

Actually that raises a interesting point, given the proliferation of nukes on anchient terra leading up to the dark age of technology I stand by my suspicion that most 40k gear is EMP hardened or at the very least all the STC stuff (which is pretty much all IG and Space Marine gear). But i stand by my previous bit, if it were such a great tactic someone would have done it already.

Considering that most wargear is made from STC's that are very very old and probably created in a time were atomics were used regulary, it is a safe bet that they are hardened against emp. So, the effects should be limited I guess.