Old Guns

Shortly after taking over The Castle, an old Minutemen, Ronnie will arrive in the Castle. Talk to her to start the this quest. She’ll Lead you to the castle’s Armory entrance. Talk to her and she’ll lead you to the northeast bastion. There’s rubble in the general’s quarters which you can clear in Workshop Mode.

It’s possible for you to explore the tunnel before the start of the quest so if you already cleared it before the quest started, things will be easier to complete this time around. Otherwise, you'll have to deal with a MG turret and a sentry bot in the last locked room named Sarge.

She’ll open the security door for you. You’ll find the former general’s body. You can loot the Minutemen General outfit and keep it to yourself if you want. Head through the door next. Follow Ronnie to the armory and get the artillery schematics from the table and the artillery smoke grenades from the crate. Talk to Ronnie once again then you’ll need to build an artillery piece. It’s best to place these on their previous locations in the corners of The Castle.

After building this, you’ll be able to call in artillery strikes on the locations where you shoot your artillery smoke grenades. An artillery piece requires one operator so assign someone to it. Once done, talk to Ronnie again and follow her to make a trial run of the artillery. You need to have the radio transmitter online before you can do this. Head to the marked location and throw your signal grenade there. Leave the area and watch the fireworks. After that, talk to Preston to complete the quest. Ronnie will also become a regular member of your settlers.