Squadmate Mode is a unique feature to the campaign mode of the Wii version of Call of Duty: World at War and Call of Duty: Modern Warfare: Reflex Edition. This allows two players to play on a single screen. The second player is "riding" on the primary player. The second player can only aim, shoot, pickup/exchange weapons and reload. This allows double the firepower the player would normally have. This is also ideal on the Wii version, if the primary player needs to reload at a tight spot, the second player can back up the first player until he/she is done reloading. This is similar to the co-op mode found in the PC, PlayStation 3 and Xbox 360 versions of Call of Duty: World at War, though if the primary player is downed, the secondary player dies too.
At the start of the mission, if Squadmate mode was already activated previously, the Squadmate will receive the same load out as the primary player. If the Squadmate joins in the midst of a campaign level, he will have no weapons or ammo.
It is advisable not to snipe as the primary player while in Squadmate Mode because the Squadmate cannot ADS and cannot shoot while the primary player is scoping with a sniper rifle. The Squadmate will still be able to shoot if the primary player is aiming down conventional iron sights or red dot sights, though the Squadmate's view will be tunneled and largely obstructed by the primary player's sights.
As the Squadmate is not able to aim down the sights, he will not be able to use or even pick up weapons in which aiming down the sights is necessary to fire the weapon, e.g. the RPG-7, FIM-92 Stinger and the FGM-148 Javelin. The Squadmate is also unable to use sniper rifles.
The Squadmate will also have no access to grenades, special grenades or rifle grenades of any kind.
Squadmate mode is not available on rail-shooting or other special missions. Such missions in Call of Duty 4 include: "F.N.G", "The Coup", "Death From Above", "Shock and Awe" (Mk 19 sequences), "Aftermath" and "All Ghillied Up". Squadmate mode will also be temporarily disabled if the primary player uses a FGM-148 Javelin, the downed minigun in "Heat" or stationary mounted machine guns.
Despite such limitations, the crosshair of the Squadmate is not affected by either the movement or the firing stance of the primary player. It is only affected by the Squadmate shooting his weapon. Likely due to an oversight by the developers, during the final sequence in "Game Over" where Price slides an M1911 to Soap, the Squadmate will be able to, in a humorous manner, use any primary weapon received prior to the tanker exploding.
To end Squadmate mode, the Squadmate should press 1 on the Wiimote.