So my gaming group is looking for something fun and different to try while we take a break from our usual games (Pathfinder and Star Wars Saga Edition) and I suggested I would run a 40k game as I love the universe. The group more or less decided to do Only War mainly because they all like the idea of playing guardsmen. However, I imagine Only War lends itself mostly to combat oriented games and while thats fun sometimes, I was also curious about possible roleplay involved.

Anyways, I am wanting to run a one shot adventures for my group (most likely 4 players besides the GM) but I am unsure what kind of adventure to run, as me and my group included have never played any of the 40k RPGs. I was thinking about a mission where the squad has been left behind on a war torn planet and have to fight to survive and escape, I am not sure what enemies are appropriate for low level heroes, but I was thinking traitor guard and I even had the idea of slipping in the option for the heroes to turn traitor themselves for an easy way to escape. Other ideas I had are that the planet is scheduled to be glassed and if they were to go traitor, a warp portal might be their only way off world.

IDK, I am looking for any ideas, as I really want to introduce this setting to my group and have them enjoy it. A one shot is ideal because this will most likely not be a long running game inless the group really enjoys it. But I am more or less looking for recommendations assuming none of us have ever touched one of the 40k core rulebooks, because honestly, we pretty much havn't.

TL;DR
Whats a good one shot adventure idea?
Is there any way the players should build their group to not hinder themselves?
Good ways to balance combat and roleplay.
Are there any rules I should deffinately know about before trying to run a game (besides character creation haha)
Any thing else you think might be useful to a new group and GM.

run Eleventh Hour. Its exactly what you want - got some social aspects, have to escape a lost conflict and get back to friendly territory, etc.

Decide the regiment together, and make sure the players are involved in that process. They can build their own version of it, or use a stock one. Either way, the Regiment should be the same so the players start with a basis they created.

If it's a one shot to introduce the setting then it doesn't matter what happens to PCs in the end right?

First Session

PCs play hive gangers. Life in the underhive is familiar and they are the big men who get to boss the locals around. But it is also quite stuffy with no chance of advancement. Senior gang members above them aren't going anywhere. The Guard is seen as a glorious endeavour. PCs have to compete with another couple of gangs to join up.

Second Session

PCs are living the dream. There is a parade and they are issued with uniforms. They get to say they are Guardsmen to friends and family. There is also a briefiing where they are told about the WH40K universe through the lens of the uplifting primer. Orks are strong but very stupid and easily confused, Tyranids are gnats who are easily swatted away, Eldar weapon is old and prone to malfunction etc etc.

Really big up how awesome the power of the Imperium and particularly the guards equipment is. Have a grizziled sgt kill a servitor with the lasgun with one shot to an eye. Have him also demonstrate the flak jacket stopping a stub revolver shot dead.

PCs engage in a mock war game vs other squads or combat servitors.

Session ends with PCs being told they are being assigned to a war zone where some humans have foolishly rebelled against the Imperium. Whole mission will be a cake walk as the rebels are facing the might of the Imperial Guard!

Third Session

The PCs are in cramped conditions on a star ship they have to deal with crazy preachers, stern commissars, hardbitten veterans and the growing feeling from the mood of officers and other experienced guardsmen that this warzone isn't going to be so easy after all.

PCs make a chilling discovery that the Munitorium have ordered body bags for 99% of the guardsmen on board.

PCs have to put down a mutiney from some veterans who try to take control of ship. Apparently they have found out where they are going and "won't go back man...In the name of the Emperor we ain't going back!"

Fourth Session

PCs board large Orbital Landers. Enough to hold a couple of companies at least. They are briefed that they are the second wave of this assault. The officers seem a bit vauge about what their objective is. Basically just saying push towards the 'gatehouse'. Apparently this will be enough information.

PCs land down. Ramps open and.....

They are met with pandemonium as the Imperial Guard regiments are fed into the meat grinder of trying to storm an Iron Warriors held fortress with predictable results.

Entire squads are blown apart from artillery rounds, heavy bolter emplacements tear through the PCs squad, every NPC they have befriended is cut down mercilessly and the only orders they are given seems to be to push towards a gigantic gatehouse, whose doors have been blasted open by a now destroyed warlord titan.

At this point simply throw a series of increasingly dangeorus foes at the PCs. If they do somehow reach the gatehouse they can be confronted with a few Squads of Traitor Marines supported by a Defiler or two. When the last PC is butchered simply read an epilouge stating that....

'18 months later and after a full 10 year siege with over seven million guardsmen killed the fortress was finally cleansed of Chaos taint. It was held by perhaps 100 traitor marines and their assorted Chaotic allies and minions. The operation was considered by the Department Munitorium to be an unqualified military success with, considering the opposition, only a relative minimal loss of Imperial assets.

Then finish by saying 'Oh...and welcome to the Guard!'

Edited August 20, 2014 by Visitor Q