Half-Life: Opposing Force/Weapons

Pipe Wrench
The first melee weapon Shephard finds, the wrench is suitable for bashing crates and enemies alike. Alternate fire prepares for a more forceful swing, that increases in power the longer mouse2 is held.

Combat Knife
Another melee weapon that is considered weaker than the original crowbar, but is very fast and effective against headcrabs or already wounded or weak enemies. Stabbing some enemies in the back can result in a one-hit kill.

Barnacle Grapple
A supposedly "tamed" native of Xen. Its ability to latch onto distant organic targets (including enemies) using its long tongue makes it useful as a grappling hook allowing the player to scale heights and cross otherwise impassable gaps. Primary fire shoots out the tongue and pulls the player towards whatever it sticks to, alt-fire stops it from retracting its tongue, allowing the player to swing around. It becomes an invaluable tool when obtaining 'ammo' for the Spore Launcher (see below).

9mm Handgun (Glock 17)
The most basic concept of a ranged weapon. It's considered reliably accurate from close up to medium/far range, and has been accredited with average stopping power. The 9mm Pistol is one of a handful of weapons in the series that can be fired underwater. Secondary fire fires the pistol in fully-automatic mode that greatly increases the rate of fire, and unlike the original Half-Life, the accuracy stays the same.

Desert Eagle
A powerful semi-automatic pistol. Similar to Half-Life's Colt Python revolver, but has less recoil and a faster rate of fire. Alt-fire activates its laser sight, which greatly increases its accuracy but reduces its firing rate.

MP5 (Heckler & Koch MP5)
Fully automatic with average stopping power. High magazine capacity and rate of fire. Has an attached grenade launcher using the same impact grenades as in Half-Life 1. Despite it using the same 9mm caliber cartridges as the Glock 17, the MP5 is noticeably less accurate, although this is normally not a problem unless trying to minimise ammo consumption at a range of medium-far. Fortunately 9mm cartridges are one of the most common ammunition pickups in most installments of the series.

Shotgun (SPAS-12)
Powerful when up close, but has a slow rate of fire, long reload time, and is next to useless at medium-long range.

RPG
An extremely powerful weapon, but must be reloaded for each shot. Alternate fire activates/deactivates a laser sight. With the laser sight on- any rockets in the area (including enemy-origin ones) will track the laser to where the crosshair is pointing. If the laser sight is off, the player fires and reloads leaving the rocket to its direction. This 'Dumb-Firing' tactic is useful on tanks and similar enemies (excluding Apaches) because you can pop into the open for an second, shoot, and get back behind cover again.

MK2 Hand Grenade
A handheld explosive. Can bounce off of walls and detonates after five seconds.

Laser Tripmine
A high-explosive Claymore mine-like device that can be attached to walls. It is set off either by damaging the mine itself, by crossing through the laser "tripwire" emitted from it, or interfering with the length of the laser (eg. breaking the box at the end of the laser).

Satchel Charge
A highly potent explosive that can be thrown a short distance and detonated remotely. Secondary fire allows the user to place additional charges.

M249 Squad Automatic Weapon (M249 SAW or SAW)
A light machine gun that is very effective at cutting down groups of enemies, but empties quickly and has a long reload time. Its powerful recoil makes it difficult to aim; crouching while firing can help alleviate this. Ammo for this weapon is extremely rare until the end of the chapter Vicarious Reality. If sufficient ammunition is available, the M249 can be used to impede falls by shooting downwards while falling. The backwards recoil will constantly push towards the player's back, regardless of direction, resulting in lower downwards momentum.

M40A1 Sniper Rifle
A powerful and accurate sniper rifle that is very effective at long distances. Its bullets hit their targets instantly, unlike the bolts of the Tranquiliser Crossbow in Half-Life. Alt-fire activates the fixed-power scope. Ammunition for this weapon is extremely rare, so pick your targets wisely. On Hard difficulty, some enemies are no longer killed in one hit by body-shots, but head-shots will still produce the desired effect.

Spore Launcher
An infant shock-trooper with a tadpole-like appearance, the Spore Launcher feeds on spores and regurgitates them as dangerous warheads. Primary mode fires a glowing green alien spore (which can be picked up from scattered "spore pods") that does heavy damage to organic enemies. Its alt-fire mode launches a slower-moving "spore grenade" that bounces around for a few seconds and then explodes, causing even greater damage in its area of effect. Shephard seems to hold some affection for the creature, stroking it fondly during one of the idle animations. Shock Troopers can use the same spores as grenades.

Shock Roach
Another biological weapon, these insect-like creatures are the standard armament of the alien Shock Troopers-which apparently bond to a host's skin with its six legs until death. The Shock Roach fires an electric bolt that inflicts moderate damage. It can only fire off ten such bolts, but continuously replenishes its "ammunition.". Firing underwater is a bad idea since it fires electricity. Shock Troopers seem to have an inbuilt resistance to Shock Roaches, who will sometimes attack other members of Race-X when their host has been killed.

Displacer Cannon (Project XV11382)
An experimental teleportation weapon, its primary fire launches a large, slow, green orb of energy that damages enemies it passes by and obliterates anything that it hits directly. In the single-player game, the alt-fire is used to transport Shephard to Xen as well as access certain "hidden" areas of the game. Both modes need 1–2 seconds to "charge". In multiplayer, the alt-fire teleports the player to a random area of the map. The Displacer's primary fire is, in effect and damage, homage to the BFG weapon of the Doom and Quake series, taking out any enemy short of a boss with a direct hit and dealing splash damage in a visible radius.

Note: The displacer uses the same spinning component as the gauss/tau gun- which can be seen when it charges a shot- and uses the same Uranium-235 as the Gauss and Gluon guns.