With Our Powers Combined

With Our Powers Combined is a quest in Fallout 4. It occurs after the ending if the player finishes The Nuclear Option and completes the game with the Minutemen, but has hostile status with the Brotherhood of Steel.

Quick walkthrough
With Our Powers Combined Objective: Build artillery in five settlement locations and launch a strike on Prydwen, defend the Castle.

Build artillery defenses after speaking with Preston. Build an Artillery Piece and later assign a settler to man it in five different settlements you own.

Once that is done, visit the Minutemen radio operator in the Castle and ask him to give the strike order. Prepare for the attack and defeat the enemy.