MINUTEMEN QUEST 04 - Old Guns
Triggered by completing a few quests for the Minutemen after retaking the Castle during Minutemen Quest 03 - Taking Independence and three days have passed.
Note: You will be fighting a powerful sentry bot during this quest, so bring along a strong energy weapon (like a laser rifle) or high damage ballistic weapon (such as a missile launcher). You may want to bring Paladin Danse for this mission as he uses an energy weapon.
Objective: Return to the Castle
After the required time has passed and you have handed in the required quests to Preston, he will tell you to meet Ronnie Shaw (a veteran Minuteman) at the Castle.
Objective: Speak to Ronnie Shaw at the Castle
When you arrive, walk over to the leathery looking old lady with a marker over her head. She will inform you about the Castle's armoury which sounds like a lost treasure trove of guns and other equipment.
Objective: Gain access to the Castle's armoury
Wandering after Ronnie brings you to the heavily locked main entrance to the armoury. Don't bother trying to open the thing here as it isn't going to budge. Ronnie will inform you of an alternate entrance to the place, so follow her into the North-East bastion. Make sure you explore the room Ronnie goes to first as there is a missile launcher and a few missiles just free for the taking on the table.
Inside the marked room, a pile of dirt and brick rubble will block your way. To get past this, you need to enter workshop mode (by holding the back button or interacting with the work bench) and press X/ Square to scrap the mess blocking your way. Tromp after Ronnie down the revealed stairs and enter the Castle tunnels.
Be warned, the Castle tunnels are extremely dangerous due to large numbers of frag mines scattered throughout the area. Make sure to pay attention to where you are walking and use the V.A.T.S aiming system to detect the mines easier. The way through is pretty linear, with a small supply room you can loot in the middle of the area (with ammo on shelves). Around the corner from the supply room you'll run into a machine gun turret, so bring it down quickly before it can fire back.
Through the doorway beyond the turret you'll see a lit machine with a fusion core you can grab. Move past the machine and through the next archway turning right at the end of the hallway. You'll enter a medium sized room with an inactive sentry bot in the far corner. This bot (Sarge) will activate and attack when you get close. You can get the drop on him by attacking before he fully powers up. If you don't have any powerful energy weapons, use the missile launcher you picked up from the table earlier in this quest to inflict some major damage.
Ronnie and your companion should rush in creating a distraction while you chip away at the bot's health bar. Make sure to target the glowing red exhaust panel on it's back if possible to deal increased damage. When it eventually falls, back away quickly as it explodes upon 'death.' Loot the wreckage for a couple of fusion cores before turning to the terminal the bot was guarding. Ronnie will open the security door for you here after an attempt or two, gaining you access to the rear area of the tunnels.
On the floor in the next room are the remains of the previous Minutemen general. Feel free to loot his outfit and hat (useful for the charisma bonuses) before entering the door to the West Bastion nearby. At the top of the stairs, push the glowing red button beside the doorway for the main armoury entrance to open up. Move further inside to find the armoury itself.
Objective: Collect the artillery schematic
Objective: Collect the smoke flares
Act like a kid in a candy store and pick the place clean. Make sure to grab the artillery schematics, parts and smoke flares. A fat man and plenty of other goodies are up for grabs.
Objective: Talk to Ronnie Shaw
When you're done looting, head back out to the courtyard and talk to Ronnie. She'll want you to use the schematics and parts to create some artillery for the Castle.
Objective: Build and assign artillery at the Castle
Trigger/ interact with the workshop and you'll find artillery emplacements under the special tab of the construction menu. Climb up to the walls and drop a couple down (you should have the parts from the armoury). You will then need to assign people (or wait for them to assign themselves) by walking over to a settler/ minuteman while in workshop mode and pressing A/X then returning to the artillery and pressing A/X again to assign them to the object.
Objective: Talk to Ronnie Shaw
Ronnie will now want to test fire the artillery to check everything's working properly.
Objective: Follow Ronnie Shaw
Ronnie will move over to a broken part of the Castle fortifications and point out the diner you met the Minutemen at before you captured the Castle during Minutemen Quest 03 - Taking Independence. This is to be the target for the bombing.
Objective: Head to the target area
(Optional) Objective: Keep your radio on and tuned to radio freedom
Stroll over to the place marked, adjusting your radio if you like.
Objective: Throw a smoke flare into the target area
Equip the smoke flare in your menu and hurl it into the diner (hold RB). Don't worry, you'll have plenty of time to clear the area before the bombardment hits. Back up a bit and listen to the radio to hear the preparations for firing. When the diner is demolished by the attack, the artillery is ready to go.
Objective: Talk to Preston Garvey
Return to Preston's location and have a quick chat for some praise and to finish off the quest. Looks like the Minutemen have some real firepower at their disposal again.