Symphony D.
Deity
1. I might note that for killing a lot of people in a localized area in a very short amount of time, for little cost, there is no more effective weapon than a nuke. It's also a terribly effective terror weapon in that after a few uses, nobody will every stand to you again. If only you possess it, all the better. Plus, such a thing is often a result of the typical "Why do it? Because we can" human mentality. That said, nukes are much more a question of if you can build them, not if you want to, technologically speaking...1. No nukes indeed.
2. I doubt that there would be tanks - the Empire's quest for global supremacy is unlikely to bog down in trench warfare, the world just doesn't fit for it, and so there will be no need for tanks.
2. Tanks are a natural enough concept to arise without trench warfare, given modernized war out of the trenches is infinitely more deadly than in them, given the terrible casualties inflicted when both sides actually managed to become mobile. You get a box that moves with a naval turret on top to go places ships can't. They were called "land battleships" for a reason, and this idea would come easily enough to an advanced naval culture, in my opinion.