After the phase out of the N80 in 2051, the N99 sidearm became standard issue military gear. The N99 was known for its ability to survive in the harshest of conditions and did so in many tests, as the weapon was able to reliably be restored to working condition after an extended period of time exposed to hard elements and without maintenance.
The N99 proved to stand up to its claims and as a result, is one of the most common weapons found in use in the wasteland. While many civilian weapons were ruined beyond use in the extreme conditions following the War, the N99 is commonly able to be easily restored to working order by anyone with even the most basic knowledge of firearm mechanics.
However, an N99 in poor condition can often deliver low target and armor penetration, frequent jamming, and greatly reduced accuracy. Fortunately, the weapon was produced in great numbers and many units are available for replacement parts.
An N99 10mm pistol equipped with a suppressor, which allows for silent kills if the target is killed with the first shot. This stealth feature comes at the cost of durability and damage, however a sneak attack always result in a critical hit, so the lower damage can be compensated for, especially with the Better Criticals perk.
Firing the silenced 10mm pistol will not increase your chance to be detected, unless the player has a very low sneak skill. It is therefore useful for killing weaker enemies like radroaches, mole rats, and sometimes even raiders, without drawing attention from other enemies. A high enough Small Guns skill makes it a useful close-quarters weapon in office building type settings, such as the Bethesda ruins and the Museum of History.
Sim version Operation: Anchorage (add-on) - A sim-only version of the weapon which has been re-skinned to appear newer and less worn. It also differs in health, with a whopping 999,150 hit points, essentially preventing the gun from ever degrading, This weapon is not normally accessible outside of the simulation.
The following is based on Fallout 3 cut content and has not been confirmed by canon sources.
10mm alloy steel pistol - Another version of the weapon was cut from the Operation Anchorage add-on, it differs from the standard 10mm pistol in appearance only, using the same new skin as the sim only version.
Sonora Cruz' 10mm pistol - a unique pistol found on Sonora Cruz. It deals a whopping 100 damage, but Sonora always flees from enemies, and never uses her pistol.
End of information based on Fallout 3 cut content.
In the caves under Oasis, after you decide the fate of Harold, head to the door to your right, there is a cave where you can find it. You cannot go back, but you can dive into the nearby water and exit via the underwater door back to Oasis.
Underwater by a sunken car at the docks near Arefu, along with an ammunition box with 10mm rounds.
Operation: Anchorage (add-on) A pre-war variant will be given to player at the beginning of the Anchorage Reclamation simulation, and will be removed after you take out the Chinese Artilleries.