I've come to the realization that no matter what I do, the Darnen will always screw me over. Even if the siege breaker was completed, their flying would negate it. The only way I will ever be able to survive their onslaught is through the use of a military. And the Townbrush military has a record for fucking up constantly. I can't really rely on a handful of badasses to defend the fort when they could all drown to death in a single day.
Therefore, I have only one option; to value quantity of quality. I have drafted every single dwarf, aside from one lowly farmer, into the military. When more migrants come, they shall also be drafted. I will continue drafting soldiers, regardless of the equipment available, until I have an army large enough to overcome the Darnen through sheer numbers. It is a crude and bloody solution to the problem, but the only one that has any chance of working. This is how Townbrush survived in its very first year. Our trained military could not overcome the Ogres, but 10 angry peasants swarming an ogre would inevitably bring it down. The same principle can be applied to any army.
That is assuming New Townbrush can survive long enough to get any migrants. We have next to no food and booze available at the moment.