I think armoured tusks were not uncommon, but a weapon in the trunk goes against elephant nature. They fight other elephants with their tusks, but tend to keep their trunks out of the way. I have seen video of a circus master getting repeatedly whacked by an elephant, so they can use the trunk to hit soft and juicy things or pulling up treas and such, but they would be much more likely to use tusks against dangerous looking sharp spiky creatures.
Elephants were notorious for being dangerous for both sides in a battle. They tended to be too smart to get into obviously dangerous situations and would end up running over their own forces. Even well trained horses will balk given enough impetus. If you really need an animal to pull a wagon load of gunpowder into a burning castle, use oxen.
A tangent on the elephant smarts tangent, I was once successfully extorted by an elephant. I offered it a peanut from a bag, and it took the hand holding the peanut in its trunk, rolled the arm until it was completely locked in a submission hold, and then gently placed my hand between two of its molars. I gave it the rest of the bag, and it let go of my arm having made its point. Definitely not an animal I would like to see with PTSD
Anyway, sorry to hear about the sword, and I would love to hear more on the topic of elephants with weapons.
Josh