Show No Mercy

Show No Mercy is a Brotherhood of Steel main quest in Fallout 4.

Detailed walkthrough
Meet Elder Maxson on the flight deck for the Sole Survivor's first assignment as a Brotherhood Knight after becoming familiar with the Prydwen and the crew.

Maxson's orders are to travel to Fort Strong, exterminate the super mutant forces and secure the armory, which will give the Brotherhood an advantage in the upcoming war.

Step onto the Vertibird and man the mounted minigun. After a short trip, the aircraft circles the area while the player character uses the minigun to kill the super mutant behemoth (and any remaining super mutants after the Vertibird lands).

Disembark and remove all indicated super mutants. Next, enter the armory and wipe out all hostiles on every floor of the building.

Talk to Paladin Danse, who decides to stay and make sure the armory is secure (one can also pass a medium speech check and ask why he hates super mutants so much).

Return to the Prydwen and speak to Maxson for a reward of Vertibird signal grenades.

Bugs
{{Notable content }}
 * {{Platforms|ps4}} If the player character destroys the Vertibird before entering, the quest marker will remain floating over where the Virtibird used to be. (Video Evidence: https://www.youtube.com/watch?v=UeTznRJxmqo)
 * You can remedy this by travelling to Fort Strong on foot. The quest will update the moment you encounter Behemoth.
 * {{Platforms|ps4}} If you destroy the Vertibird, then reload a save, the Virtibird will return to the Prydwen's docking bay. (Video evidence: https://www.youtube.com/watch?v=UeTznRJxmqo)
 * {{Platforms|ps4} It is possible that the player may be unable to board the quest designated Virtibird. Interacting with it causes nothing to happen in such cases. (Video Evidence: https://www.youtube.com/watch?v=UeTznRJxmqo)
 * You can remedy this by travelling to Fort Strong on foot. The quest will update the moment you encounter Behemoth.
 * {{Platforms|pc}} Companions, particularly Paladin Danse, may fail to board the Vertibird if the player enters first. To remedy this, it is advisable to order the companion to board the Vertibird first.{{Verify|16:55, December 24, 2015 (UTC)|type=bug}}
 * {{Platforms|pc|ps4}} After getting the quest and talking with Elder Maxson, the marked Vertibird to take you to Fort Strong does not appear. If you quit and reload, it will appear but won't allow you to enter. You may need to take the Vertibird on the opposite side down to the ground underneath and then back up to the flight deck to hopefully be able to use the marked Vertibird. Saving and reloading does not resolve the issue. This can be resolved on the PC using the console:  open the console, click on the Vertibird and type {{Console|activate player}}. Loading a save from before you first exit The Prydwen can fix this issue on PS4. {{Verify|16:55, December 24, 2015 (UTC)|type=bug}}
 * {{Platforms|ps4}} If you forego the Vertibird because it is not allowing you to enter, you can go on foot to take Fort Strong and complete the quest.{{Verify|Verified}} However, if you have a companion with you, the companion will remain on the airship flight deck and you can no longer talk to them. Swapping out companions will always result in the new companion leaving you (wherever you are) and appearing back on the airship flight deck. Quitting and reloading does not work. To resolve, summon a Vertibird using a grenade obtained from Maxson and enter. After landing, the companion should be with you again. Waiting in the command deck sometimes fixes the issue.{{Verify|16:55, December 24, 2015 (UTC)|type=bug}}
 * Another bug happens when the player has cleared out the Fort Strong Armory. The next objective is to speak to Paladin Danse.  When the player engages Paladin Danse, he immediately attacks and he will take no damage.  If the player fast travels to the Prydwen, the BOS will also attack the player instantly.{{Verify|16:55, December 24, 2015 (UTC)|type=bug}}{{pn}}
 * {{Platforms|pc|xboxone}} Trying to shoot while on the Vertibird doesn't work. The bug actually occurs a bit earlier (not able to display/shoot with weapon) by recruiting Paladin Danse as your partner. Using the text dialogue to go alone usually fixes this bug.{{Verify|16:55, December 24, 2015 (UTC)|type=bug}}
 * {{Platforms|pc}} After clearing the first section of the Armory, the V.A.N.S. Perk and the quest marker tell you to go outside. Exiting Fort Strong Armory and returning to turn the quest in will not work. You must enter the elevator car in the East corridor to proceed to the larger testing area to finish clearing mutants. You will then be notified with a quest update and Paladin Danse will show up (if not a companion) as you exit this area to comment on the results.{{Verify|16:55, December 24, 2015 (UTC)|type=bug}}
 * {{Platforms|pc}} Sometimes the Vertibird will not show up, and your quest marker will tell you to take the Vertibird to Boston Airport. Saving and reloading may fix this.{{Verify|16:55, December 24, 2015 (UTC)|type=bug}}
 * {{Platforms|pc}} If you ask Paladin Danse to accompany you for this mission then choose your previous companion instead, once securing Fort Strong, Paladin Danse may spawn on the lower level of Fort Strong as though he were with you all along.{{Verify|20:03, January 7, 2016 (UTC)|type=bug}}
 * {{Platforms|ps4}} Sometimes when entering Fort Strong the elevator will be bugged. The elevator will descend upon entering but the doors will not open, trapping the player inside indefinitely. Solution: Restart console and load a save aboard The Prydwen.{{verify|type=bug|20:48, January 11, 2016 (UTC)}}