The bipod is equipped on the Browning M1919 and MG42 portable machine guns. Going prone with any of these and deploying the bipod allows the player to aim down the sights, otherwise they can only be hipfired. The bipod is also present on the DPM support weapon, but this weapon can be aimed while standing without deploying the bipod.
The bipod is equipped on the M1919A6 and the MG34. Unlike Finest Hour, aiming down the sights will automatically make the player go prone and use the bipod, or attach it to a surface if they stand near an appropriate one. The weapon can still be fired from the hip in other instances.
In the campaign, the bipod is only found attached to the Browning M1919, Type 99, MG42 and FG42 (the latter two are always equipped with a bipod in campaign). The player can zoom in while mounted to aim down the sight on the gun that the user is upholding. The first-person model of the BAR in campaign depicts the weapon with a bipod, but it is unusable (though the third-person model shows it without one).
The bipod is available on completing the first Marksman challenge (Marksman I) for all MGs, which requires 25 kills. It is more effective for MGs that can hold more ammo, as weapons such as the BAR, Type 99, and FG42 contain too little ammo and/or fire too fast to effectively use the bipod for prolonged periods of time.
To mount a machine gun, go up to any leveled surface (e.g. a windowsill or sandbags), and a message saying "press and hold 'use' to mount weapon". The bipod can only be used when the message shows up, and it can no longer be used while prone.
Using the bipod on some machine guns like the DP-28, Type 99, or BAR, decreases the machine-guns' iron sight zoom. The MG42 and Browning are apparently not affected by this.
The reticle will change into a large white cross when mounted, which will even appear in Hardcore. Recoil and idle sway are completely removed when the bipod is mounted, but there is also somewhat limited horizontal turning range. Firing from the bipod also causes the gun to appear to shoot 2-3 rounds, however this is simply an animation bug as pulling off single shots results in the gun appearing to fire multiple times. The bipod is often used to create a distraction or provide extremely effective covering fire.
There are no permanently mounted machine guns in Call of Duty: World at War's multiplayer. These were removed in favor of the much more mobile bipods.
The bipod is present on all of the machine guns in both Nacht Der Untoten and Verrückt (except for the Nacht Der Untoten version of the BAR). However, there are only two places where it is possible to mount a bipod. There is one mountable surface near the "whispering morgue," where the BAR is bought off the wall, however, this position is practically useless. The other is near the balcony on the German side, though it can only be done in co-op. If a player crouches near the balcony in a certain spot and the other with the weapons that has a bipod holds the use button near them, it will mount on top of their head, and will remain even after the other player leaves the spot. The bipod was removed in Shi No Numa and Der Riese, though the weapon model of the BAR and the FG42 still shows a visible bipod.
In Nacht der Untoten and Verrückt, there is overwhelming evidence that there was once the option to mount the player's machine guns in various places, such as the sandbags upstairs on Nacht der Untoten or the balconies of Verrückt, but was scrapped by the developers. This is further supported by the mounted guns found under the map in Verrückt via noclip, the bipods physically present on the weapons, the weapons names (i.e. Deployable BAR as opposed to just BAR), and in the Verrückt trailer, a Marine is seen using a Browning M1919 mounted in a window.
It appears usable by the player in the mission Ops M.I.A., where it is mounted on the Dragunov, and can be seen used by enemies throughout the whole campaign on LMGs, as they sometimes mount their weapons.