They are a set of fast-paced missions in the spirit of "Mile High Club" from Call of Duty 4: Modern Warfare. Originally meant to be the co-op portion of the story campaign, it was spun off into it's own separate game mode as Special Ops. This also allowed the designers to add new levels that were interesting or reuse existing levels with expanded or new objectives without having to fit them into the single-player campaign's storyline like the campaign missions. The missions can be played solo, split screen or online with a few being two player exclusive (Needing two players in order to play.)
The Special Ops mode was created after Infinity Ward attempted to insert co-op into the main single-player campaign mode. Infinity Ward said that they wanted to keep the two man feeling from "All Ghillied Up" to have each others' backs and cover each other and work together to complete the objective. They found out that attempting to make single player missions co-op compatible was less fun than a regular single-player mode and broke the feeling of immersion that they are going for. However, instead of scrapping a co-op mode entirely, they created the Special Ops mode with all levels tailored for two players.
Both players could not die at the same time. For example, if a grenade rolls next to them, one will always survive the blast.
In an oversight for both games, the dialogue said by the playable characters when reloading includes "Changing mag!" and "I'm out!", even if their weapon doesn't have a detachable magazine or wasn't empty.