Tactical Thinking

Tactical Thinking is a quest in Fallout 4.

Quick walkthrough

 * 1) Speak to Lancer Captain Kells
 * 2) Enter Old North Church
 * 3) Kill Doctor Carrington
 * 4) Breach the door to the lower levels
 * 5) Kill Glory
 * 6) Kill Tinker Tom
 * 7) Kill Deacon
 * 8) Kill Desdemona
 * 9) Reprogram P.A.M. or destroy her
 * 10) Report to Kells

Detailed walkthrough
If wanting to get kicked out of the Railroad, accept Kell’s forthcoming orders and this becomes permament, so if you have any loose ends to tie up with the Railroad, do so before speaking to Kells. You’ve been informed that Lancer Captain Kells wishes to speak with you on the command deck of the Prydwen. After agreeing to his orders, head north into the North End neighborhood of Boston, and enter the Old North Church. You have a Priority Kill Order list. It's time to check those priorities off.

Remove all threats in the initial church chamber. It's wise to eliminate all foes before continuing into the crypt. Fight down into the catacombs. Locate and activate the detonator and blow a hole in the wall. Your remaining primary targets are now acquired.

Enter through the hole in the wall and into the Railroad HQ. Dispatch all Railroad threats from the theater of combat

Locate the P.A.M. mainframe terminal or the automaton herself. Either destroy the robot or use the terminal to reprogram her. Then return and report to Kells.

There is disappointment if P.A.M. was deactivated rather than reprogrammed. If she was reprogrammed, she is later transported onto the Prydwen.

Bugs

 * Deacon may appear shortly after you enter Old North Church, and if you kill him before the quest tells you to, it may not count towards the objective. Reloading to a save prior to entering Old North Church might fix this. Alternatively, speaking to Knight Captain Kells once you've completed all other objectives may still allow you to turn the quest in.
 * Deacon may become unkillable, unselectable in VATS but still shooting back. Use setstage BoS302B 120 and report back to Prydwen to finish the quest.
 * Detonator may not appear, rendering the mission impossible to finish. Using tcl command to go through the wall and kill Carrington fixes the problem.