The Desert Eagle is a powerful sidearm that holds seven rounds of .357 ammunition. While somewhat similar to the .357 Magnum revolver at first glance, there is a major difference between them; the Desert Eagle has two firing modes. The first one, automatic, is the primary firing mode. It fires much faster than the .357, but is less accurate. The second mode is activated by hitting the alternate fire key. This activates a laser that makes the weapon as accurate as the .357, but decreases the rate of fire, although it stays faster than the .357's.
This weapon is first obtained in the middle of the chapter Welcome to Black Mesa, where a Black Mesa security guard dies by electricity shock when trying to open the generator gate near the crashed Osprey Heliplane. If not obtained there, it can be acquired by killing HECU Engineers who will drop them. It is also possible to acquire it even earlier in the chapter, where the first security guard is encountered in the infirmary. Although the Shephard has no weapons at this point, it is possible to hold the security door open (that the security guard opens once the PCV is acquired), by placing a (nearby) movable chair right up next to one of the doors. If done correctly, one can run around the corner to pick up the pipe wrench (where the security door would normally close to prevent back-tracking), go back and kill the security guard and take his weapon.
- The Desert Eagle can kill anything weaker than a Bullsquid in one shot. While this may sound tempting, it is better to conserve Desert Eagle ammo for foes that require multiple Desert Eagle shots to take down, such as Shock Troopers and Pit Drones. All of the enemies that can be killed with one Desert Eagle shot can also be killed with one double shotgun blast, which has much more ammo scattered throughout the game than the Desert Eagle does.
- The Desert Eagle works best at medium-long range, so the laser sight should be activated at all times.
- When close to an enemy, the laser sight should be turned off. Rapid firing does more damage at close range than taking timed shots with the secondary fire mode.
- In Hard mode, it takes around two shots to take down enemies that used to take one, so headshots are essential for conserving ammo.
- This weapon is extremely effective against Black Ops. It usually takes about two aimed shots to defeat one Black Ops soldier in Normal mode, and the Desert Eagle can engage them at long range, a range in which Black Ops' weapons are less effective.
- Caution must be exercised while having the laser sight activated, as enemies can see it in the dark.
- In older versions of Opposing Force, the Desert Eagle's laser sight can be used to redirect a rocket fired with the RPG, and vice versa.
- It can clearly be seen that the Desert Eagle viewmodel has no iron sights. This may be because it uses a laser dot to aim, however it would be highly impractical for a laser sight to be the only way to aim a firearm. Interestingly, the worldmodel for the Desert Eagle has visible iron sights, which is odd considering the fact that worldmodels are generally less detailed than viewmodels.
- It should also be noted that, in the real world, the .357 magnum version of the Desert Eagle has a 9-round magazine, as opposed to 7-rounds as depicted in the game (the .50AE version, however, does have a 7-round magazine).
 List of appearances
- Half-Life: Opposing Force Teaser (First appearance) (Non-canonical appearance)
- Half-Life: Opposing Force
|Hazardous Environment Combat Unit|
|Characters||Minor members · Dwight T. Barnes · Sharp · Adrian Shephard|
|Classes||HECU Engineer · HECU Medic · HECU Sniper|
|Weapons||9mm Pistol · Artillery Cannon · Combat Knife · Desert Eagle · Dynamite · Fragmentation Grenade · Gun Emplacement · Land Mine · Laser Trip Mine · M249 Squad Automatic Weapon · M-40A1 Sniper Rifle · Mortar · Submachine Gun · Rocket Cannon · RPG · Satchel Charge · Sentry Gun · Shotgun · Tripod-Mounted Heavy Machine Gun|
|Transportation||AH-64 Apache · Jet · M1A1 Abrams · M2A3 Bradley · M44 cargo truck · Osprey Heliplane|
|Technology||Chargers · Powered Combat Vest · Radio · Tactical Map · Transportation · Weapons|
|Other||Hazardous Environment Combat Unit models · Military Police · Robot Grunt · Santego Military Base|
|Classes (cut)||Human Sergeant|
|Weapons (cut)||20mm Cannon|