I think we need to find out what some of the other notes [if there are other notes] said, they might reveal a little more information.
Guardia had some interest in technology, judging from the Dragon Tank. They didn't necessarily use it for war either, so why'd they build that machine? It may have been for defense, or it may have been an idea that Yakra put forth, who knows, but Guardia had some interest in technology at one point, while Porre definitely seems to have pursued it to a higher degree.
Also I think I've gotten too into the idea that this is weaponry, it's also possible that this could have been something simpler: gunpowder, steel, a raft (like FaustWolf said), food...the possibilities are endless. Lucca was resourceful, maybe she decided to turn her resourcefulness into a pretty penny to fund her orphanage, or something.