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 actually be found during gameplay), in addition to the restrictions seen in multiplayer below. Unlike in multiplayer and Zombies, the Chicom CQB, FAL OSW, SMR, SWAT-556, M8A1, Colt M16A1 and FAL are fully-automatic by default, but with the Select fire attachment they can be switched to burst fire or semi-automatic mode, depending on the weapon.
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 a single or burst weapon will reduce accuracy and increase recoil. Likewise, using burst fire on a fully automatic weapon reduces recoil and thus increases accuracy. This is a result of the attachment altering the centerspeed (the time it takes the sights to reset to their previous position after firing a round) of a weapon its attached to, and varies between weapons. Using this on the FAL OSW, SMR, SWAT-556, and M8A1 will lower their centerspeeds, thus increasing recoil. On the other hand, using Select Fire on any fully automatic assault rifle will increase their centerspeeds, making them more accurate.
Select Fire on SMGs behaves in the same way as on assault rifles, though recoil changes vary between some weapons in the class. The MP7 gains no recoil decrease when used in burst fire mode as its centerspeed remains the same. Interestingly, using Select Fire on the Chicom CQB and firing in full auto does not come with a centerspeed decrease (and thus recoil increase); this is because its normal rate of fire is a maximum of 1250 RPM, and when in full auto this drops to only 937 RPM.
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.
Here is shown the delay between bursts for weapons gaining a burst mode when equipped with Select Fire. 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 noticeably reduced for most weapons.
A variant of the Select Fire attachment appears in Call of Duty: WWII, added on June 25th, 2018 with the 1.18 patch update. It can only be found as an integrated attachment featured exclusively on the ZK-383. It allows the player to switch between the gun's "Slow Firing" and "Fast Firing" modes.
In most SMGs and assault rifles used in the past missions, there is no sound when using the Select Fire switch.
In full FOV, (Max. 90), it is possible to see the player's thumb in both Campaign and Multiplayer switch the fire modes, yet the switch does not move on the gun model. It can be commonly seen on the MP7.