In Call of Duty 4: Modern Warfare, it was set to appear on the assault rifles, as proven below. In Call of Duty: World at War, it would have allowed players to switch the fire mode of the STG-44, M1A1 Carbine, and SVT-40 between semi-automatic and full-automatic. In Call of Duty: Black Ops, it was shown to be initially available as an integrated attachment for the Galil. Although this feature was present in Call of Duty and Call of Duty: United Offensive, it was cut from subsequent games due to lack of real use.
It is mentioned in the Call of Duty: World at War strategy guide, which was published before the game's release.
Select Fire is available at the start of the campaign. It appears as an attachment for all assault rifles (in both timelines) and the submachine guns of 2025 only. In campaign, it cannot be paired with Rapid Fire, Suppressor or Long Barrel in the customized loadout (though some of these combinations can be found during gameplay), in addition to the restrictions seen in multiplayer below.
Select Fire is available for assault rifles and submachine guns. It adds a more controllable burst mode to fully automatic weapons, and a full-auto option to burst and semi-auto weapons. Keep in mind that adding and using full auto mode on single or burst weapon will always reduce accuracy and increase recoil. Likewise, using burst fire on a fully automatic weapon reduces recoil and thus increases accuracy.
Maximum fire rates of the semi-automatic rifles, the FAL OSW and SMR are lowered from 625 RPM and 535 RPM to 468 RPM and 416 RPM respectively for balancing reasons, similar to how the CZ75 had its maximum rate of fire reduced from 625 RPM to 535 RPM when equipped with the Full-Auto attachment in Call of Duty: Black Ops. The SWAT-556 also suffers from extreme loss in range, being able to kill in three hits on fully automatic in only point-blank.
In previous games, almost all burst-firing weapons had a delay of 0.2 seconds between bursts, but in Call of Duty: Black Ops II, the delay has been reduced for most weapons. In campaign, all burst-firing weapons have no delay between bursts (excluding the M1216, since it is technically not a burst-firing weapon, but automatic and rechambered after each four fired rounds).