What's the use in an old fort without suitable armaments? After taking over Fort Independence in Taking Independence, it's time to dress up the place with some firepower. Like clockwork, a military vet, Ronnie Shaw, arrives to show you the fort's useful facilities. Those include a secret underground area and an armory.
Follow the waypoint indicator to the pile of gravel blocking one of the paths. Activate workbench mode to remove the obstruction. Head down the path and through the door. Once inside, move with caution. There's a lot of loot to collect, but there are also a lot of mines to dash from. And there's a heavily armed Sentry Bot to watch out for. When you've eliminated the bot, Ronnie will open the security door, leading you to the armory.
Once inside, take whatever weapons and gear suits you. You also need to pick up some artillery smoke grenades to advance the quest. Go into workshop mode and create an artillery turret, an option located under the Special category. Then highlight any unnamed Minutemen soldier, and assign the turret to that character.
Follow the latest waypoint indicator and toss a smoke grenade in that direction. Ronnie would also like a field test of the turret. Let the test firing play out and note that you can use these smoke grenades to call in attacks outside this quest. Conclude this quest by speaking to Preston Garvey.