Call of Duty 4: Modern Warfare is a first person shooter game that was developed by Infinity Ward and published by Activision in November 2007. The game, changed quite drastically in development with a substantial amount of cut content, far more than other games in the series. While these levels are rendered unplayable in the release builds, early builds have arisen with several of these cut levels fully playable, while others remain unavailable, indicating that they were cut earlier in development and never existed in a playable form. (on the other hand, some missions included in the final game were only finished months before launch, so hope remains.) Footage of several of the cut levels was published by YouTube user UHDGaming in 2016 from Xbox 360 pre-alpha build 328, but seemed reluctant to release the build to the public. (probably due to copyright concerns) Later, in 2018, user Adryonic posted footage from an earlier build, build 253.
A devkit is required to play the pre-alpha builds.
It was originally planned that the training mission would have taken place with the USMC, as opposed to the SAS. The level retains many of the objectives that were seen within the FNG mission featured in the final game. The level is removed from the final build, with only the compass file and the strings file, (containing objectives, prompts to the player, and so on) being preserved. A fully playable version of the level is seen in the pre-alpha build. Seen in this level are several characters that didn't feature in the final game, as all missions containing them were removed, such as the playable character Michael Carver.
On build 253 of the game, this mission was dated 2nd March 2007.
The original mission was longer than that seen in the final product. After finishing weapons training with Gaz, instead of going straight to Cpt. Price for the CQB course, the player would have had to first go to Sgt. Newcastle for explosives training, and then complete an obstacle course. These were cut so late in development, the obstacle course and explosives pit can be found in the final game, just with the objective triggers removed. They were restored as optional objectives as part of Modern Warfare Remastered.
The exact name of this level is unknown, but is given this name as the game's mod tools refer to the assets in the level with
cobrapilot. The level was referenced in some promotional material for the game, so was clearly cut quite late in development.  The level can be found fully playable in the pre-alpha build, with even button prompts, controller layouts and sound effects prepared for the level. (albeit, at this point in development, a bit crudely presented)
On build 253 of the game, this mission was dated 16th November 2006, suggesting it was among the first missions to be developed.
Almost nothing was known about this mission (all that remains in the final game is the compass file) until videos of the pre-alpha builds surfaced. In both builds 253 and 328, the level is incomplete. The objective at the beginning says "Hunt down Drago Zakhaev", though there is no dialogue thereafter. It is suggested that this was an early name for the character Victor Zakhaev, as evidenced by a few filenames. The mission has players destroy vehicles and push through a school, though as the level is unfinished little happens after that. Some helicopters are spawned at the end of the level, though they are not scripted to do anything, suggesting that the player may have escaped by helicopter.
The mission is dated 9th March 2007 on build 253.
This level does not feature on any found early builds. There is, however, a string file, descent.str, in the mod tools of the game. The level would have taken place in Riyadh, Saudi Arabia, quite late in the game. The string file suggests that the Marines were to enter an underground bunker, where Al-Asad (spelt Assad in the string file) had either been murdered by an officer, or committed suicide. The game would have had the player use a camera, which still exists in the final game, though the models no longer exist in the game files. The reload button would have zoomed in the camera, and the shoot button would have taken a photo. In the final game, Al-Asad is killed by Captain Price in his safehouse in Azerbaijan.
The string file still contains placeholders from Call of Duty 2, possibly suggesting the level was cut early in development.
The level was thought to have never existed in any playable form, with only a .vision file to evidence its existence. However, it is found playable in both builds 253 and 328. The player spawns near a helicopter, where several friendly NPCs are spawned. They are however not scripted to do anything and have no collision detection. No objectives are programmed for the mission, nor any dialogue, so it's unknown when in the game this mission would have taken place, the plot, or which characters would have featured. The player spawns with only the default weapon, and no enemies are spawned. The player can explore forest, a graveyard, and some ruins where more inactive NPCs can be found. The level then abruptly cuts off into the void.
Embassy is a level found in build 328. It however fails to load either due to an issue with the level, or due to the fact that the level was never completed to that point. No remnant of the level exists in the final game.