So, I just had my first second third invading force while using Fortress Defense.
I'm coming back to DWarf Fortress after having not played for a year. I used to play with Dig Deeper, but that seems to have been abandoned and from looking around the forums, Fortress Defense seems to be the new "go to" mod.
My first Dig Deeper fort, six months after embark, ~20 orcs with exceptional quality steel weapons showed up and slaughtered my outnumbered dwarves. My second Dig Deeper fort I discovered that orcs were TRAP_IMMUNE. It took quite a few obliterated forts to learn how to cope with that, and when installing Fortress Defese, I pretty much expected to get killed in the same way while I learned how to cope with not just orcs, but ten new hostile civiizations.
Apparently Fortress Defense is a kinder, gentler mod than I expected. Which is probably not a bad thing, but here is the tale:
In the flatlands fortress of Girderpass, shortly after Summer of my second year I saw the dreaded siege warning:
A Vile Force of Darkness has arrived!
I checked the list and saw that I was under attack by a group of 9 tigerpeople: 8 swordsmen and one hammerer. When I first installed Fortress Defense I had briefly glanced through the monster descriptions, and I was pretty sure that tiger people were the third of the new civilizations. So having apparently skipped over the first two, I figured I was pretty much done for. But nine was a much smaller a force than I expected, so I didn't completely lose hope. I began gathering up my dwarves, only to discover that the "Dwarves Stay Indoors" setting of previous versions has apparently been removed, and resigned myself to losing several craftsmen, if I even managed to stay alive at all.
A Vile Force of Darkness has arrived!
What, seriously? The first invasion force hasn't even reached my front gate, and another siege arrives? Dark stranglers, apparently. With two siege armies arriving at once, I figured I was pretty much toast. The 14 dwarves of my military were in position aboveground, behind the arrow-blocking wall inside the keep, waiting for the onslaught. A few assorted craftspeople decided now would be a good time to randomly wander around outside. Oh well. Wasn't expecting the fort to survive. A few early deaths would just speed up the process.
An ambush! Curse them!
You're kidding, right? Two sieges and now goblins show up? I didn't even bother checking the list of new arrivals and just sat looking at the carefully constructed chokepoint leading to the only entrance to my soon to be doomed fortress, as the pack of tiger peoples charged up to it...
...and then suddenly turned and ran away before even getting in range of my military.
Apparently they're not trap immune, and when the first several had assorted arms and legs sheared off by iron serrated discs, the rest lost interest. I remembered reading in the notes that the first couple new civiliations weren't TRAP_IMMUNE, so I wasn't totally surprised that the traps hurt them, but with Dig Deeper I remember orcs would sometimes spend months locked in an auto-repeating upright spike trap room, outhealing all damage. So I wasn't really expecting that little 3x3 field of weapon traps to repel the entire siege.
As for the others, they never got that far. The stranglers and the goblins decided to ignore me and fight each other, and after a few deaths they both ran away too. Leaving my military wondering if that year they spent danger-room training was really justified.
Snatcher! Protect the Children!
Umm, ok. Sorry dude, you're a little late to the party. Never saw what happened to the snatcher, but between two sieges and an ambush not a single one of my dwarves was injured, and there were surprisingly few corpses. The vast majority of the attackers ran away at first blood. Checking the combat logs I saw a lot of trap dodges and parries, so I'm not totally sure but I think the first few made it past the weapons traps to the first row of stonefall traps, but by the time they did, some of the invaders further back started dying to the weapons traps, and then the whole group decided to turn around and leave, going back over the weapons traps a second time. I think that's how the tigerhammerer died.
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So, looking to the future, I'm much less concerned about being hopelessly slaughtered than I was. From Dig Deeper I'm used to massive sieges of armored, TRAP_IMMUNE orcs weilding high quality steel weapons. Pages and pages of invaders, so strong and well equipped and numerous that pits and drowning chambers and spike rooms and lava are the only practical way to deal with then. I' used to having 50% of my dwarves trained as multiple legendary champions in steel armor...not to repel sieges, but just in case a couple slip through the fixed defenses.
In retrospect, Dig Deeper was probably too much. The orcs came in such numbers, so soon, and so well equipped that there was basically no way to have a military deal with them. You could embark with 7 military dwarves and do nothing but train until the siege came and still die.
Fortress Defense looks like it offers a much more reasonable pace, with simple monsters at first, and gradually growing to tougher and more difficult ones.