Enemies originally were to be marked with blinking corners, or, they were made for debug. This can be enabled through console.
The AC-130's gunner has multiple recorded lines, but almost none of them are heard in the final game, apart from notifying the player when the 105mm gun has been reloaded.
Originally there were three objectives: "Get radiation equipment", "Locate commanding officer" and "Find secure overhead cover."
All Ghillied Up
In the E3 trailer and in the first screenshots from the game, Cpt. MacMillan was carrying a silenced M4A1. This picture can be seen on the back of the game's box.
In localization strings, the level originally was called "Zones of Exclusion", it was placed in 1995, and the player started with a Barrett .50cal instead of the M21.
Look through the Internal files, and one will find a Sound Folder called Villagedef. Look for a file with something like this "Villagedef_SAS2_7_16". It consists of an SAS member saying: "I owe you one mate. Thanks for coming back for me." Gaz also has unused audio from the mission, where he states: "We got a man down!!! He's still alive!! And he just activated his transponder!!"
Mile High Club
According to the cut audio files for the level, the hostage's name was supposed to be Kriegler.
Some unused audio files shed some light on the mission's purpose:
airplane_gaz_1_1_R has Gaz saying "Remember, the objective is to capture Kriegler, I repeat, capture Kriegler, alive. He's no good to us dead."
airplane_gaz_7_2_R has Gaz saying "Watch your fire up here, we need Kriegler alive."
airplane_gaz_9_1_R has Gaz saying "Nice one, Soap."
airplane_gaz_9_5_R has Gaz saying "We're going for a little free fall Kriegler! On your feet!"
In earlier E3 2007 footage, Paul Jackson was originally in the 1st Battalion 7th Marine Regiment prior to the unit being changed to 1st Force Recon.
In a Single Player demo video, Vasquez uses an M4A1 Grenadier rifle, rather than a M16A4.
An unused audio file for Griggs has him saying "You shoot just like Jackson!"
Another one has him saying "Who said there was no such thing as a Black Russian?".
Some scripts for the cut missions mention a character named Michael Carver who was the original USMC protagonist, replaced by Jackson in the final build.
A screenshot released by Infinity Ward shows that Price was originally going to be featured in the Marine campaign.
In the E3 2007 demo of Call of Duty 4, Gaz was originally named Griggs.
The News Caster has some unused audio: "The Russian government released a statement today confirming the death of Imran Zakhaev. According to several reliable witnesses, the Ultranationalist leader, who started the brutal war in Russia, was killed while attempting to evade Loyalist troops at a safehouse in Grosme."
The AH-1 Cobra was intended to be fully flyable as shown by the files "cobra_controls1.cfg" and "cobra_controls2.cfg". One can also find a string labeled "cobra_player" within the files.
The mp weapons folder show the 25mm, 40mm, and 105mm weapons for the AC-130, suggesting it was originally going to be implemented as a killstreak for multiplayer. The weapons are inaccessible via devconsole however. Attempting to use effects and sound effects from the weapons in other weapons will cause the game to crash while starting a server.
There is an unused model of an AC-130 in the games' files, suggesting that it was going to be used somewhere in the campaign or in the multiplayer mode.