USMC

The United States Marine Corps (USMC) is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States. In the civilian leadership structure of the United States military, the Marine Corps is a component of the United States Department of the Navy, often working closely with U.S. naval forces for training, transportation, and logistic purposes; however, in the military leadership structure the Marine Corps is a separate branch.

In Call of Duty 1, 2 and 3
They fought in the World War II against the Axis in many battles and many places, one of them being France during the D-Day.

In Call of Duty 4: Modern Warfare
General Shepherd sent more than 30,000 marines to Iran to find Khaled Al-Asad. The game centers in the marine Sgt. Paul Jackson, soldier in the 1st Force Recon under the orders of Lt. Vasquez. The team fails to get Al-Asad and a nuclear device explodes killing all the marines in the area. After the marines were killed, the SAS begun an operative with the USMC to stop the Ultranationalists. At the end of the game, dies the last of the known-in-game marines, SSgt. Griggs.

In Call of Duty 5: World at War
Pvt. Carlson Miller was rescued by his teammates, after being captured by Japanese soldiers. The USMC begins with an attack to Okinawa and ends taking the Shuri Castle.

In Call of Duty 6: Modern Warfare 2
They're just mentioned two times: First time when the Task Force 141 are operating in the Oil Rig, and then when Shepherd mention them at the end of the game to Soap Mactavish.

In Call of Duty 7: Black Ops
Captain Alex Mason and Sergeant Frank Woods are USMC soldiers, and SOG operators. USMC marines can be seen fighting in Khe Sanh against the NVAs in the Vietnam War. SOG Operators are USMC marines and CIA agents.

Multiplayer
USMC are a multiplayer faction that always fights OpFor.

Maps:
 * Fallujah
 * Baghdad
 * Mosul