Fallout 4 - Accessing Fort Independence's Armory (Artillery)

Once you get the word from Preston to go back to The Castle (Fort Independence) meet up with Crazy Ronnie and she'll take you to the armory and help set up some artillery defenses. Mission is called "Old Guns" You only need to set up 1 piece of artillery then assign someone to it...I made 3 thinking they would tell me when to assign someone.