The Magnum is a default starting weapon of the player in all three Marathon games. Able to be dual-wielded, the pistol is very useful in the early stages of the game as it is the only ranged weapon the player has. It retains its usefulness into the later stages of the game, especially when a second pistol is acquired (used via the secondary fire button). The pistol has a scope (no game effect) and is one of the more accurate weapons throughout the game.
The .45 and .44 can both fire in a vacuum, but not underwater.
"Standard issue for all security officers and active duty field personnel. Utilizes 8-shot clips of .45 caliber high velocity, vacuum enabled teflon rounds (teflon maintains stable flight for accuracy). Titanium construction results in a sturdy, reliable, light weight firearm."
- from Marathon manual
"The new standard issue sidearm for all field personnel doesn't look much like your old .45 MMC, does it? That is because it has been built for a single purpose, by a dedicated people and not by underpaid laborers toiling for a thinly-veiled government-owned arms manufacturing machine (oiled with the blood of the underclasses, by the way) which exists solely to line the pockets of the greedy bureaucrats who run the military/industrial complex."
- from Marathon 2 manual