Black Crusade has an interesting way of running large battles involving hundreds of NPCs, with flexibility in regards to the involvement of the PCs. The system is different from the one in Rogue Trader, for example. Anyone have experience running it? How did it go?

We had run a slave camp siege with it. Players attacked the camp. First They Basilisked the ShÍt out the defence lines (Flak towers mainly, and a big @ss Martello Tower) after it they rushed in with 2 Malcador and 1 Leman Russ tank and some Ifv (2 Chimera 1 Rhino). The shelling was Navigate skill checks. Commander done some command skill test to move and order the troops. Meanwhile there was a dogfight between allied pirates and the enemy planes. Form the dogfight they had got reports and act to it as it was in another scene. When the fights had taken place between two horde, I used the Tome of Blood rules (more or less stylized). I had told the story in narrative but granted chance so they could change it. If they went in the battle we done it as regular horde rules and other stuffs.

I've used it a few times. It works and tends to produce nice narrative effects without tieing things down unlike resolving it as a fight between multiple huge-magnitude hordes.

Make sure both sides can push their effective combat skill up to the 40's or the whole thing (a) takes ages and (b) is too random, despite the player's efforts. And make sure there are some enemy 'generals' doing the same thing on the other side - identifying them and dealing with them makes for ideal turning points.

I tend to split up mass combats into two or three 'fronts' fighting simultaneously. That way each player (or pair of players) handles one 'front' or 'flank' or whatever, and it doesn't just turn into a dice-fest, plus you don't get six players all throwing skills and infamy points into the fray such that the stats of their actual troops become irrelevant (or if they do, they do so by sacrificing the troops on the other flank, which is their own choice and perfectly acceptable!)

I'll let them use pretty much any skill, as long as they narratively describe what they're doing.