The arsenal key is used in B1F, close to the end of the game. Use the Blue Emblem obtained from the Security Room and the Red Emblem from the sleeping gas room (block the vents with the rocks, then open the box) on the out-of-place red and blue orbs in 1F southwest.How do you get the rocket launcher? I have the arsenal key but cannot for the life of me find where to use it. All I see is keycard 3 locks and rubble that needs a shovel.
Keycard 3 is from the kennel event, so if you're meeting progression fuckery bugs around that point you may need to load an even earlier save...