Old Guns

Old Guns is a quest and achievement/trophy in Fallout 4.

Quick walkthrough
After receiving the quest, head to The Castle and talk to Ronnie Shaw. She'll guide you to the old General's room where you need to use the Workshop to clear the rubble. Inside, you'll find a turret and Sarge.

After defeating Sarge, open the door with the button on the wall and take the Artillery schematics.

Make the Artillery, assign somebody to it, and throw an Artillery Smoke Flare in the target location.