You ' ll Know It When It Happens You ' ll Know It When It Happens is a in " " . Detailed walkthrough . The Courier will be directed to speak with Ranger Grant in order to make preparations . Speaking to him will trigger a wait period , after which it will be time for the speech . He will allow the player character to make a security sweep before the speech begins . If the player character is not in good standing with the NCR he will not give the Courier the itinerary for the speech and the player character will not be allowed to draw their weapons even if intending to kill the sniper or engineer . The Courier may ask Grant for access to all areas of the dam in order to do a proper search . At this point , the player character may either complete the optional objective or skip to the speech . Optional . Investigate the area for clues . There will be no waypoints to direct you , so you must locate them manually . Note : If you have Boone as a companion , when you walk up the ramp on the visitor center exterior towards Ranger Grant he ' ll say something about if he were the sniper , where he would shoot from . He ' ll tell you 3 locations ( he is correct about the last two ) : The speech . Once you speak to Ranger Grant again , the speech will begin . Kimball ' s Vertibird , Bear Force One , will land on the roof of the Visitor Center . Kimball and four Rangers will disembark , then move to the stage for the speech . In order to hear the entire speech , each assassination attempt must be dealt with quickly and covertly ; alternatively there are opportunities to scuttle the speech early to get the President to safety . Keep in mind that even if you asked for and received clearance to enter " all areas " from Grant , entering the backstage area or going onto the stage with the President will cause the NCR to become hostile . There are three different assassination attempts : If you received this quest from Yes Man or Mr . House , the staircase leading to the roof of the visitor center will be locked . However , so long as you ' re in good standing with the NCR and asked Ranger Grant for access to all areas , you can go up using the ladder on the outside of the building . Private will be guarding it , so an NCR disguise might be necessary to bypass him . A disguise can be found in the storage closet underneath the stairs in the visitor center . You can also talk your way past him with a Speech skill of 50 . The same can happen if you have a mixed relationship with the NCR even if you attain this quest through the NCR . Once on the roof , depending on how quickly you get up there , you may see an engineer tamper with the Vertibird . " Activate " the Vertibird to examine it , which will reveal that a bomb has been planted on it . An Explosives or Repair skill of 50 is required to remove it . Failing that , you ' ll need to get the detonator from the engineer . This can be done before or after the arrival of the sniper . He ' ll head into the crowd watching the speech , so you ' ll need to find him . He is on the left side facing the podium . The right ( or left , depending on whether you are watching from the visitor center or the guard tower ) engineer is the only one who will talk to you , and is the only one who won ' t clap . He will also move around occasionally , as noted in some cases . If you have in your company he will detect the Legion engineer in the group , growling at him to point him out . Talking to the engineer will turn him hostile , thus canceling the speech . If you have the Animal Friend perk , you can take the search dog from the Ranger in front of the visitor center . The dog will also sniff out the disguised engineer . Whether or not you have been able to defuse the bomb , you still need to stop the assassin at the guard tower . You will see him throw the real guard off the guard tower and take his place , unless you ' re already there , in which case he ' ll attack both you and the real guard on the spot . If you ' ve missed the event , there are several ways to tell if the assassin has come . First and foremost , the ranger ' s body will be on the ground in front of the tower . It can be examined to determine that the ranger was killed recently , but cannot be looted until after the quest is completed . Second , the assassin , though dressed similarly , has a visible face . The ranger wears a face wrap . Finally , the ranger will remain in position near the radio on the tower , while the assassin will pace back and forth . About halfway through the speech , the assassin will line up his shot , firing after a few seconds . Finally , the Legion engineer may attempt to stab Kimball personally . This won ' t happen if you covertly disable the bomb , since the engineer will still try to detonate it . Assuming he does attack , kill him and the final assassination attempt will be foiled . Kimball will return to his Vertibird and depart , completing the mission . Alternate completion methods . There are a few other methods with which you can end this quest . However , each of these methods yields a different ending to the quest . Note that , no matter which way the quest is solved ( as long as NCR doesn ' t turn hostile on you ) , you will receive the Eureka ! quest ( if you are siding with the NCR ) . All of them involve canceling or interrupting Kimball ' s speech .