Party is fighing a mercenary unit trying to topple a neighboring realm. The party runs into trouble at the new border check points, Rebels offer to pay the Party to help them topple the region, but the unit is flavored to be an actually competent Lawful-Evil military force with uniforms and everything. To give the party a narrative weakness to exploit, the unit is a core of elites & veterans supplemented by mostly greenies, convicts, and local recruits (who are just bandits). There was a small theme of the convicts and locals being used as cannon fodder by the elites, and growing resentment about that. I some notes to be fleshed out if the party did any looking at that what so ever, they'd quickly see the locals and criminal brigades (or at least section) could be convinced to sit out the fighting or even change sides. Party of course gives zero shits about the people they are killing - which is fine, and why it was just notes.
Anyway, the individual elements had unit names & mottos, individual uniforms, officers & NCOs auto-generated. I had exact numbers of soldiers just incase they wanted to wage a war attrition. Everything in place just in case the party doesn't want to solve the problem with murder, because one of the players before the campaign starts has been going on about how great it is that D&D lets you think outside the box to solve problems and you don't always have to fight everything. So I make sure they have low-combat (well, low party involved combat) path to success. I later learn what meant by this was they just start combat by telling the enemies to surrender.
Anyway, they are players so naturally they only use violence to solve their problems, which is the expected path. After cutting a bloody swath through the ranks of the invading force, they finally get to attacking their HQ. They did almost perfect in the approaching assault. Cut off their fortified base from reinforcements. They knew about the secret passage through the walls. Sliiiightly fuck up using it, but not in anyway that brings immediate negative consequences. Basically every tool for success they could get (without talking to or observing their opponents), they had so its not like they are in a desperate situation. Then after they burst in to the first room, murder everyone, and while still covered in blood from those guys... only then does one of the party members say "Hey! What if we try to blend in and tell them we're part of the garrison?". This is the final chapter - I'm not fleshing out those notes and everyone and everything is ready for the assault. There is no reasonable way for the party have any useful social knowledge and its already been narratively conveyed that everyone has dogtags and names recorded in a roster. I suggest to them "You don't know anyone's names, you talked to one prisoner, and everyone is on edge because they are beseiged, and you think you can bluff your way in?". They still want to do it, so I let them try, and naturally they fail at the first "What unit are you with?" because they never so much as bothered watching a check point to see how they interact with each other. Rather than let them continue to flounder and fail, I have the NPCs start combat because they have zero chance of success and they're just dragging things out.
Half the party gets pissy about being "Railroaded" when the response of soldiers in a besieged fortification to strangers in torn and blooded uniforms who don't answer to challenges as expected is to draw steel.
For my part I was cutting them more slack than they should have gotten when making their initial breech (noisy entry, noisy battle, but it was on a different floor and was trying to give them rewards for thinking because they sent the non-clanking mage in to make the first kills) and so apparently they felt they had been given expectations of being able to metal gear solid the whole area. So I should have been consistent in rulings and had the guards in the next area attack them in the breech room. And I also made the NPCs a little more trigger happy than they might have been, starting combat instead of sending a runner to a commanding officer, because that was just going to drag things out for the same conclusion.
They also got pissy because I guess I was supposed to have read their minds and didn't give them quest markers about how to let them do the ground work to be able to implement this idea before they had come up with it.
