Tradecraft

Tradecraft is a quest and achievement/trophy in Fallout 4.

Detailed walkthrough

 * 1) Talk to Deacon about things that need to be done, you can pass a set of 3 persuasion checks of increasing difficulty to find out that he's had his eye on you already.
 * 2) If you accept the job Deacon asks you to meet him at the old highway, the marker is roughly between Drumlin Diner and Rocky Narrows Park.
 * 3) Deacon has remade himself, talk to him a bit and then head off on the mission.  Along the way you'll get some info on "Rail signs", directions given through graffiti.  There will be ghouls on the way.
 * 4) Once you reach the "tourist" give him the password and get the recon report from him, then talk to Deacon again.
 * 5) You'll be given the choice of a frontal assault or going in through the old escape tunnel.

Option 1: Escape tunnel

 * 1) Go back to where you met Deacon and then head for the quest marker, if you haven't picked it up yet there's a suit of power armor on the train you go past.
 * 2) Once you enter the tunnel you're given a little more information about the Railroad and the target.  Shortly after the talk you'll find a Master level terminal you have to hack to proceed.
 * 3) Once past Deacon will point out a railsign that there's a cache nearby, it's in the back of the tube directly behind the sign.  Around here Deacon will warn you to just run if you meet a Courser, foreshadowing?
 * 4) Ahead there will be an unlocked terminal you can use to turn off the spotlights and turrets.
 * 5) Once past that group you'll be given a chance to turn ON some defenses that will give you an edge against the next group of enemies. Shortly after that you find out that the Railroad was using an old DIA site as their HQ.
 * 6) Next to the door leading out of the office area you go through there's a terminal you can use to turn off the tripwires in the next room.  Before leaving grab the fusion core in the room left of where you first entered and a Covert Operations Manual on a desk in the room up the stairs.
 * 7) If you go right there's some bathrooms with a synth and a locked door with some loot.  After that go left to continue the mission.
 * 8) A little further along you'll hit an intersection, left leads to the mission marker, right to the "databanks" and straight to the front door where you would have arrived otherwise.  The databanks room has some background info and locked doors with a terminal that yield minor loot.
 * 9) Once you enter the last room before the marker Deacon will open the vault and inspect a dead body, after the inspection he'll offer you the "hand cannon" the dead man used and won't take no for an answer. Grab the prototype and head towards the elevator. Before you leave, to the right of the small set of stairs leading to the elevator is a locked door with an advanced lock where you can find another fusion core.
 * 10) Once out of the elevator you get to kill all the synths you would have had you gone in through the front door.  Once they're dead Deacon will go his own way and you can go back to the church to meet him.
 * 11) Once back to the church you find Deacon lying to Desdemona, you have the option to tell the truth or pass an easy persuasion check to go along with the lie.  Once you join, or not, the mission is complete.

Option 2: Frontal assault
If you choose this option you will fight through all of the synths and the turret stationed at the front entrance as well as have to pick up all of the mines on the ground, however the power to the elevator that leads to the basement will be shut off so you'll have to go through the back.

Quest stages

 * Talk to Deacon
 * Meet Deacon at the old highway
 * Follow Deacon and find the "tourist"
 * Talk to Deacon
 * Get inside the escape tunnel
 * (Optional) Enter base through the front entrance
 * Get Carrington's prototype
 * Leave the Switchboard
 * Meet Deacon at the Old North Church

Bugs

 * Deacon might stall in the hallway outside the room containing the locked vault and the Inaccessible terminal. Save and Reload may clear this.