Enclave soldier (Fallout 3)

Enclave soldiers are the main infantry of the Enclave, and are the toughest, strongest, fastest and most well-equipped human enemies the player will face in Fallout 3. Their equipment is superior to even the advanced armor and weapons used by the Brotherhood of Steel. Because they are the direct descendants of the US Army, Enclave soldiers also benefit from professional military training and communication systems.

Enclave officer
Enclave officers wear standard Enclave officer uniforms and hats. They are armed with plasma pistols, and carry plasma grenades as backup.

Enclave trainee (rank 0)
Enclave trainees can be found at certain Enclave outposts after The Waters of Life, doing push-ups under the supervision of an Enclave officer. Trainees are equipped only with laser pistols; they do not wear helmets, and their power armor is in extremely poor condition.

Enclave soldier (rank 1 & 2)
Regular Enclave soldiers wear Enclave power armor, and are usually armed with laser rifles and laser pistols. On rare occasions, they can also be equipped with flamers or Rippers. They also carry a random chem, like Psycho or Buffout. After downloading Broken Steel, these particular soldiers become rarer (especially at higher difficulty levels and after completing the main questline) compared to Enclave soldiers with Tesla armor or Enclave Hellfire armor.

Enclave Tesla soldier
As their name suggests, these Enclave soldiers wear Tesla armor, and are usually equipped with plasma rifles. They may also carry miniguns, Gatling lasers, or missile launchers.

They become more common at higher levels, and can replace regular soldiers in Vertibird drops. They also appear in fixed locations (such as in front of Alexandria Arms), or as Colonel Autumn's bodyguards. They are considerably tougher compared to regular soldiers, thanks to their superior armor (which is usually at near-top condition, no less) and their tendency to carry heavy weapons more often than other classes of Enclave soldiers.

Enclave Hellfire troopers (Broken Steel)
Enclave Hellfire troopers are a new variant of soldier added by the Broken Steel add-on. They wear Enclave Hellfire armor and are equipped with heavy incinerators. They also carry a plasma pistol as a sidearm.

Enclave soldier (Hellfire armor, Broken Steel)
The Broken Steel add-on also adds regular Enclave soldiers armored in Enclave Hellfire armor. They wield plasma rifles and have the same stats as the Hellfire troopers, but are just called "Enclave soldier" in-game. At the Very Hard difficulty level, they are tied with their Tesla armored comrades in being the most common Enclave soldiers (it seems equally likely to encounter both varieties). This can be a problem for unprepared players, due to their tough armor, hard-hitting plasma rifles, and large amount of health. It does, however, make spare parts for your own Hellfire power armor easier to come by.

Appeareances
Enclave soldiers appear in Fallout 3. They can also be spawned using the console in Fallout: New Vegas

Bugs

 * Occasionally Enclave soldiers and Enclave officers found randomly in the Wasteland will appear as friendly to the player. If you speak to them they will either say "Hey there." or "Yeah?" and the only dialog option is "See you later".
 * Tesla armor-wearing Enclave soldiers carrying missile launchers are always initially friendly towards the player. They will only turn hostile if they see the player fighting against other Enclave forces.
 * If the player enters Enclave occupied Project Purity before 'Take it back!', which can be done through glitches or console commands. Solution: The only way to fix this is by shooting the Enclave soldiers.
 * If the player follows one of these friendly Enclave soldiers to an Enclave camp, they will become hostile and attack the player, but no earlier than the soldiers and officers of the camp.
 * Sometimes the shield across the bridge which allows access to Project Purity to the north will not be active and the player can cross right over it and the previous bug will happen. Solution: As this is not a game inhibiting bug there's no way to fix it.
 * It is possible to see Enclave soldiers way before they are supposed to appear in the Wasteland, even at the very beginning of the game. This seems to trigger much more commonly if a player were to play a game where the Enclave is present, and then load or start an early or new game. Often still, the Enclave soldiers will respawn in certain locations as if it were an Enclave checkpoint, minus the proper Enclave structures and gear.
 * Sometimes random Enclave soldiers will appear in the wasteland before they attack and invade Project Purity. They can be killed and looted as usual, though they are extremely rare to find.