I had set up a fort in what turned out to be absolutely perfect steel country - a magma pipe, marble flux, plenty of trees, and about a dozen magnetite deposits. On top of that, I got a legendary weaponsmith and a legendary armorer quite early on - before I'd even got my steelworks up and running to full capacity. I was very proud of the industrial monster I built; I channeled magma directly to each of the magnetite deposits so the magnetite could be smelted into iron bars on-site, hauled back to the fort already in bins, and then run through a second set of smelters next to the wood furnaces and marble quarry to make steel.
The only downside of all this activity was the insatiable demand for wood. The forest was productive enough, but cutting it down and hauling it inside required a constant stream of dwarves braving the outside and resulted in a steady stream of goblin ambush casualties trickling back. A spiffy military wouldn't help much because the ambushed dwarves would be dead by the time they got there, and walling in the forest was unfeasable.
So anyway, I decided my best bet was to equip every adult dwarf in the fortress with a masterwork steel battleaxe by setting them all as woodcutters. The annual spring wood harvest would become a settlement-wide festival of lumberjacking, a vacation from their toil at the smelter banks, furnaces, and hauling paths. But masterwork axes weren't enough, in my opinion; I wanted them well trained in their use as well.
I had about a hundred dwarves, almost all completely unskilled in military matters. Setting them to spar with masterwork axes would have resulted in carnage. So first I had my legendary armorer produce a hundred complete sets of steel plate mail and shields. I would set my entire population training in wrestling, armor use, and shield use for the winter season (aside from a skeleton staff of support dwarves to keep the booze flowing and care for the inevitable injured). It took a full year of preparation to ready the fort; supplies had to be produced and laid in, perishables cleaned up and stockpiled, the brand new gigantic barracks cleared of rock and furnished. It took more than a month just for everyone to get dressed in their armor.
Finally the winter of sparring was ready to commence. I set my heavily armored dwarves off duty and they began the festivities. Mere moments later: a force of darkness has arrived!
Heh heh heh heh...
"Change of plan, boys," the lead champion of my small standing army announced to the legion of new recruits. "We're going to do axe training straight away after all. Armok has provided us with the perfect sparring partners."
With the enormous value of all the arms and armor my fort had produced I knew a siege was inevitable, so I'd built some good defenses into the fort's structure. There were two widely-separated entrances, one leading to the forest and the other coming out in the rocky ravine the brook had cut through the mountains, connected by a long underground road so that the caravans could use either of them to reach the trade depot deep in the mountain's heart. I let the siege in through the forest entrance uncontested, and then once the last goblin had passed the threshold I threw the levers to slam the gates behind them and open the other entrance's gates instead. The only way out now led straight through the heart of my fortress, where a hundred gleaming steel-clad dwarves waited for them in the trade chamber with axes at the ready.
I have never seen a trade depot that was so awash with blood and pieces of bodies before or since. Partway through the massacre a titan showed up and came in through the back entrance, but I barely even noticed when it was dispatched along with the rest of the invaders. I had to convert the brand new barracks into a goblin morgue to keep the fort from being flooded with miasma.
No dwarves died. No dwarves got much training either, though - the goblins were shared between too many and died too quickly for that. Oh well. I delayed the training plan for a year while the cleanup operation went on and the next year I got my wish of ambush-proofing every dwarf in my fort. Thereafter any time there was a goblin ambush the lone dwarf who was ambushed had a good chance of simply wiping out the ambush party on his own initiative. I just wish they'd wear their armor when going lumberjacking or wood-hauling, too.