Dreadnaught Chest Keys
There are two ways to get yourself a key to one of the Dreadnaught chests. The first is as a random drop from enemies on the Dreadnaught. The second is to pick up a Wormsinger Rune, which is a drop from Hive Knights and Hive Wizards. Remember to have space in your inventory for the Rune and to use the key as soon as you get it as you can only ever have one at a time.