The military knife is a single-bladed knife, used for close-combat, though it is still considered one of the most powerful weapons of the respective games. Enemies with 120 or less health can be instantly killed, without alerting the whole group or horde of the player's presence.
Despite seeming like the most underwhelming weapon in Sam's arsenal, the military knife should never be underestimated. Not only does the weapon have a slightly longer range than one would expect, but the 120 damage it deals per slash is devastating to all but the largest of enemies.
The knife should be used only to silently kill smaller enemies or wound bigger ones. For example, the Sirian Werebull requires only three slices, which means one could preserve ammo by using the knife.
The knife should never be used for stronger enemies, such as Major Bio-mechanoids or ranged opponents.
The knife is heavily effective against both types of Gnaars and Scythian Witch-Harpies, with the capability of killing them with one swipe. Against Kleers, two slices will do. The knife does more damage per minute than both shotguns, so it's a good alternative when the fighting arena is spacious for evading enemy attacks.
If combined with Serious Damage in The Second Encounter, the knife can be a very devastating weapon that can almost kill medium-powered targets.
In the early version of the game, it was possible to change the position of the knife in the hands. When used like this, the knife could deal much higher damage to enemies and gib weak enemies like the Rocketeer. While useful, the impact speed is noticeably lower than in the original. It was removed when the public test demo was released.
In Test 1, the knife could be swung at a faster rate, though it dealt less damage.
In Test 2, the knife's damage was increased substantially, being able to gib enemies from across the room, which was likely an oversight. The knife was later nerfed to deal 120 damage in the final release.
Though NETRICSA states that you can use the knife for stealth attacks on enemies from behind, this isn't usually possible most of the time, as enemies are alerted to the player's presence even if they are behind them.
If the knife is ported into Serious Sam 3: BFE with the use of mods or hacks and the player enters third-person view, they can see that Sam will use the same animations as the sledgehammer when using the knife.