Band Of Brilliance

The G18 is the sidearm when using the Snowmobile in Cliffhanger, and can be found in some of the levels such as "Takedown" or "Loose Ends". In multiplayer it is a highly effective short-mid range weapon, but has huge upwards recoil. Its firing rate is on par with some of the LMGs, making it both powerful and difficult to control in full auto. It can have the Red Dot Sight, Silencer, Akimbo, Full Metal Jacket, and Extended Magazines as attachments. Unlike most pistols, the G18 is held in one hand and arguably bridges the gap between the game's semi automatic and machine pistols in terms of handling (i.e. draw and aim down sights time), which can make it a competitive option for a sidearm. If wielding akimbo Glocks, one should fire both pistols in bursts to increase the accuracy.

Trivia

• Strangely, the G18 is fired with one hand in-game. In real life, if you tried firing a Glock in full auto mode with one hand, you would be hard pressed to hit anything.
• The Glock is extremely accurate with the Akimbo attachment, with one of the smallest hip-fire aiming reticules out of any Akimbo pair (of machine pistols), and even smaller with Steady Aim. This makes it a highly effective weapon at close to medium range.
• The Glock is held in the left hand on the snowmobile, when seconds before Roach got on, he used his right. This is because the throttle on a snowmobile is on the right side of the handlebar. The hand with Glock on the snowmobile is rotated 90 degrees clockwise because of better aiming at lower-placed targets (such as foot-mobiles or enemy snowmobiles) behind the windscreen (in standard grip your hand cannot be so easily bent down).
• A Glock pistol (not necessarily the Glock 18) is the icon for the Last Stand perk in Call of Duty 4: Modern Warfare.
• The gun was incorrectly modeled in Modern Warfare 2, as it does not have the Glock 18's characteristic selector switch on the side of the slide. The gun is actually a Glock 17 converted to full auto as Glock 18s were never offered in olive drab, but Glock 17s were.
• The Create-a-Class picture lacks the extended magazine found in actual gameplay, although the magazine might have been taken out to save space. (With a 32 round magazine, 33 round magazine or a 49 round magazine, even if the bullets are double stacked, you'd need an extended magazine, about 13 inches long. The picture shows the Glock with a standard 17 round magazine.)
• When the Glock's slide is locked back and the gun is reloaded, the slide release isn't used. Instead, the slide is pulled back farther and released (known as 'slingshotting'). This is the recommended method of releasing the slide from the Glock manual, in order to minimize wear to the stamped steel slide catch. Only on the snowmobile and when using akimbo (dual-wielding) is the slide release used. 
• If you look at the gun through the sniper scope on the slide it actually says Gluke instead of Glock. This is presumably for copyright reasons or just a simple mistype.
• On Infinity Ward's official website, the Glock 18 was voted the favorite machine pistol in Modern Warfare 2.
• In campaign some enemies fall into Last Stand with the pistol, but fires it semi-auto. It changes to full auto once you pick it up from the dead enemy.
• When sprinting with the G18, the camera oddly twitches to the side, although it's hardly noticeable unless you are running with Marathon.
• The pistol's sights unusually combine both the Three-dot profile with a dot-border profile found standard on Glock pistols. In real life, the dots are usually tritium night sights which allow for low level aiming.
• All Task Force 141 use the G18 as a sidearm, explaining why Roach has one in Cliffhanger's snowmobile escape, but it is odd that a person will carry two sidearms, but it is plausible because the holsters can be placed one per leg.
• When you are at the snowmobile, the Glock seems to have unlimited ammo. You still have to reload, but you cannot reload the loaded gun - you must empty the whole magazine.
• Interestingly, G18 has 32 round magazine in Single Player and one more bullet in Multi Player. This may have been a fault, but 33-round mags do exist in real life.
• When using a weapon, such as a sniper rifle or a burst fire rifle, poorly suited for close quarter fighting, a Glock 18 Akimbo(and possible Blinged with Extended Mags) can make a very powerfull close quarters sidearm.