I Hear You Knocking

I Hear You Knocking is a side quest in Fallout: New Vegas.

Quick walkthrough
Lucius wants you to get a replacement firing mechanism for the Legion's howitzer from the Boomers in Nellis Air Force Base.

Detailed walkthrough

 * 1) You access this quest at The Fort after you talk to Caesar and speak with his subordinate Lucius. From there talk to him until you reach the question about whether or not Lucius has employment opportunities. He will then explain that the Legion recently obtained an artillery weapon (which is aimed currently at Hoover Dam), but they do not have the part to fix it. He then tells you about a tribe of people called Boomers who are obsessed with such weapons.
 * 2) In the northeast corner of the Mojave Wasteland you will find Nellis Air Force Base, and after some careful running and dodging artillery fire you will be stopped by a Boomer guard. If you then agree to go willingly with Raquel she will take you to the eldest of the tribe, Mother Pearl. Talk to her and you can ask her for the firing mechanism, but she won't be so willing to part with it. After questioning you will have free roam of the base. There is a way to get the mechanism without stealing it. Become accepted by the Boomers and then ask Mother Pearl for it.
 * 3) Once you exit Mother Pearl's barracks head for a row of curved corrugated buildings and enter the second building from the end. Once inside look for the Gun cabinet in the corner, open it, and among other items you will find a Howitzer Firing Mechanism. Take it and return to The Fort. It's located in the Nellis Workshop, between Loyal's house and Nellis Boomer Museum where you can find Peter.
 * 4) When you return, search out the Howitzer on the cliff. Examine the Howitzer and replace the firing mechanism.
 * 5) Return to Caesar's tent, and inform Lucius that the howitzers have been repaired. You will gain Caesar's Legion fame as well as 100xp.

Behind the scenes
This quest is named after the song "I Hear You Knocking," probably the best known version being that of Fats Domino.