Running an Only War campaign, and I'd really need some tips and ideas.

Current party is:

One Cadian Weapons Specialist, ordinary rifleman type with lasgun.

A Death Korps Heavy Gunner, armed with a heavy bolter. Or well, he did, but the bolter was lost and he's now got a lasgun.

A Valhallan Medic, carrying a lasgun.

And finally, another Weapons Specialist built to be a sniper from a homebrew regiment (Basically Scots in Space). He's got a longlas.

Basically, the party's a group of survivors of a nuclear bombardment (someone initiated scorched earth tactics when Imperial defence was breaking down), and the idea I have is that they'll be trying to find a way off the planet, or at least to survive and hopefully find a way off it.

First session started out well, they fought some orks, we established a bit about the planet and the conflict, and then the nuclear strike happened. Having found shelter, they then stayed in there long enough to avoid the worst fallout, and then we plan on leaving the shelter next session.

Now, I have some ideas for what they might encounter (surviving Orks, other Guardsmen [hostile and friendly], things like that), but I need some tips for what else to do.

Despite being modern day technology, nuclear attacks seem very rare in 40k. I'd emphasise how incredibly destructive and contaminating the calamity is. Everything is stricken and damaged and irradiated.

I'd want to run a survival horror type affair with them needing to keep finding medication to fight the radiation and fresh air canisters for void suits or rebreathers.

Water purification tablets are a thing in 40k.

I'd be venturing that nuclear fallout has fried most of the ways you can recharge those las cells; the local grid and most generators out of commision. You can charge em up in a fire, but fresh and reliable cells will be valuable.

Basically run it as the above-ground parts of Metro 2033. Orcs, burnt and screaming in pain, but still mainly preoccupied with killing whatever they can get their hands on. Devastation and possibly psychic echoes of the dead and dying. Or hallucinations that you are having because of shock, trauma, contaminated food and limited oxygen.

Rumours of an evac that might be true.

The blast waking up a bunch of Necrons that had been running dormant.

An AdMech outpost that was moderately shielded. Hardware is still running but all of the priests died in the strike.

Something in the computer core could be the surviving consciousness of the head techpriest, or something that was meant to stay contained (AI?)

Demons brought close to the surface by the extent of the death and mayhem.

There's the usual post apocalyptic trope of running in to other survivors, the real monster is other people thing. Though I'd be more inclined to try and tempt the PCs in to robbing the other survivors rather than having the NPCs screw them over. No real reason, but my default approach is to have untrustworthy seeming people be usually trustworthy. I don't want the players to get in the habit of assuming NPCs are evil, and it just makes the rare betrayal more worthwhile.

I'd run it as a low supply, deep behind enemy lines sorta game. One thing to consider is that it is within the characterization of the Imperial Guard to continue fighting over a recently nuked planet. Maybe they hook up with battle elements who tread the nuclear devastation as business as usual. Maybe they end up in command of some slapped together group still tryign to take objectives or a convoy or survivors trying to fight their way towards some believe evac. Or maybe they just stay on the planet for months or years in isolation fighting until they finally figure a way our or they all die. Or even mixing and matching some of these together.

Lots of ways you can go with this idea, good luck!

Great ideas, so far!

The survivors of an entire city have lost faith in the Emperor and now worship an idol (insert avatar of the Chaos Gods here). This may lead to some possessions and some demon invocations.

Some detachment of the local PDF made themselves strong in a bunker/supply storage specificaly designed for big catastrophes like the nuclear attack. Now they are not opening the gates of the fortress to anyone and will fight to death to protect their stronghold.

A small Sister's Monastery has survived to the attack. It is located in a remote place not known by many. A couple of the sisters travel around the planet looking for souls and bodies that have not been corrupted by the disaster in order to take them to the safety of the Monastery.

A group of survivors are wroking in a whole new society based on cooperation . They are lacking the punch to protect themselves from the Ork raids. The player characters may help them or even declare themselves new kings of the place.

Sorry, can't hold my ideas back...

The nuclear attack has uncovered some ancient catacombs/tunnels that had been long forgotten . In these passages, a whole gretchin civilization has been hidden for ages. This may be the origin of the ork infestation in the planet, and an oportunity for the players to root it out.

Radiation + some nasty chemicals that were being used with in food growing factories have had some impressive effects in the rat population of the sewer system of one of the planet's cities. Rats are reproducing faster, grow bigger and are evolving into something more intelligent, more omnivorous and hungry. For now, only giant rats have been spotted, but rumours of an anthropomorphic.anthrophagic rat have been heard.

The ecuator of the planet is still impassible by foot or surface travel: a perpetual radioactive storm fries everything that goes below the clouds. Some towns in big mountain ranges have been able to survive the nuclear attack, but are now struggling with ork aeroplane raids. Recently, though, one group of air-pirates have been saving the day here and there, dogfighting with the orks, transporting goods and messages but also doing a bit of robinhoodesque robberies and assaults. No one knows where this people have come and, most importantly, where they got their strange-looking airplanes. Most of the rumours, though, come from the tattoo that their leader has in her forehead: a skull inside a cogwheel.

And now, some fast ideas involving surviving Guard regiments:

- one regiment with noble origins was about to retire into a promised planet after this campaign. Seeing that they may not be able to reach their promised prize soon, they decide that they are the most suitable new rulers of this planet.

- one regiment full of fanatics thinks that they are all doomed and that the nuclear attack has signaled everyone with the mark of chaos. They decide to exterminate the few survivors left and, after that, commit suicide.

- one regiment stranded in the wilderness, surrounded by orks, decides that the best opportunity to survive is to serve these orks as slaves and mercenaries.

That looks cool. Thanks for the ideas.

I'm thinking I'll put their comrades into a formation under their command depending on what they think, to have them be of some extra use, by the way. I'm thinking a formation of four extra lasguns might be some more use than +5 BS.

I've already made up a list of all their resources and plan on keeping careful track of these, and I'm wondering whether giving them a Chimera (might be one with a broken weapon, or not) would be a good idea. It'd involve keeping track of fuel and thus having them scavenge for that too, but the increased mobility might help in actually getting them around.

Thoughts?

That sounds like a really cool idea. As long as you've comfortable GMing for(enemy vehicles/dozens of infantry etc) and around(there's a underground supply cache with more promethium but it's not big enough for vehicles) the Chimera it should be sweet. There's a few ways you could go about getting it to them as well. The can find it sitting there in the open the luck of the Empra on their side. You could have them stumble upon it in the middle of a pretty intense shootout, and let them turn the tide. You could have them scoping one out, and working to capture it from hostile forces.

You also have the consideration of when you bust it out on them for the first time, and how you rule it. Whether it's at the very start, climax, or end of a session, or anything else. Like how familiar are your guys with vehicle rules, how long will it take to catch them up, and even how strongly you're going to stick with them. Some people get a bit more abstract with it, and while I like the rules how they are. In the interests of speed being a bit abstract the first time they play with it might go a long way towards pacing and tone setting the first time they get their mitts on it, especially if it's towards the end of the session but there's NPCs yet to mulch.

Food for thought. Anyway you go about it, it sounds like you got a pretty decent handle on things.