Just had a 75 unit goblin siege, 1 troll squad and 4 or 5 goblin squads, all mounted on cave crocodiles.
Versus my 5 or 6 legendary military members plus their students, totaling about 30, no traps or other fun stuff, just home-forged dwarven copper equipment.
The dwarves met the goblins from the ramparts, firing bone and copper bolts from the fortifications to the east and south, trying to inflict some wounds on the advancing army. Most of them were not carrying any ammunition (damn) and weren't very skilled, but did manage to get a few wounds in. The rest of the army waited around the corners of the southern wall, but they realized two squadmates weren't present...
They were outside the walls, trying to pick up gear! The military scrambled to meet the goblin forces at the main entrance, only to find a speardwarf dead, and the legendary sworddwarf, Sodel Startheaters. Startheaters was standing over the corpse of the speardwarf, fighting not one, but THREE squads of bowgoblins mounted on cave crocodiles! Wave after wave of bolts he dodged, getting bowled over constantly by the crocs, rising just in time to avoid another barrage from the riders. The only wound he suffered was a cut to his left arm.
The rest of the military caught up a few moments later, and began fighting off the other 2 squads, helping Startheaters with 2 other squads. The troll group and a few goblins began making their way into the main fort, seeing that my military had their hands full. I ordered the military back to the main entrance by the trade depot, and they slaughtered their way back, wading over goblin and cave crocodile corpses, with the occasional troll thrown in.
Three trolls managed to make it into the fort proper, only to be met by the crossbow-armed populace (probably why my marksdwaves had no ammo). The trolls met their match, bone bolts piercing their hides and breaking their bones, keeping them in place until the military arrived and finished the job.
A lone goblin was spotted running across the desert landscape, and orders were given to let him run. Better to have one survivor tell the tale of copper-clad dwarves cutting through an invasion force like a hot knife through butter than let the psychological warfare chance go to waste.
A few dwarves are injured, a few missing minor limbs, four died and will be dumped into the magma sea, to keep necromancers from raising them. Two of the dorms have been turned into makeshift hospitals, and any dwarf with medical experience has been told to help the wounded in any way possible. Thankfully we have a few bars of soap produced, and easy water from the aquifer just under our feet.
Now to dump the goblin corpses into the magma, and butcher the mounts, and stockpile the gifts from Goblin Christmas.
EDIT: One of the cave crocs had a native platinum gizzard stone. Wow.