With Our Powers Combined

With Our Powers Combined is an optional Minutemen quest $$ It occurs after the ending if one finishes The Nuclear Option and Old Guns and has or gained hostile status with the Brotherhood of Steel.

Detailed walkthrough
Build artillery defenses after speaking with Preston. Build an artillery piece and later assign a settler to man it in five different settlements the Sole Survivor owns. 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. Watch from the Castle, as the Prydwen is destroyed, and then prepare to fight the vertibirds that they send.

Behind the scenes
The quest name is a reference to the children's TV show Captain Planet and the Planeteers, which frequently uses the lines "by our powers combined" and "let our powers combine."

Bugs

 * The quest may halt at 90%.
 * This can be resolved by finding the last Vertibird around the Boston Airport and destroying it, triggering 100% completion. May also be fixed by reloading a previous save or by running away from the Castle and/or fast traveling to another location.
 * The quest may also stall when you need to speak with Ronnie Shaw. Every time you try to speak with her she will ask if you want to trade.