The AT4 is mentioned in the localization files for the singleplayer portion of Medal of Honor. It is never used or shown.
The AT4 is the standard rocket launcher for the Spec Ops class in Multiplayer. The AT4 has a high damage rate and can be used at long range, as it is powerful and accurate, and has virtually no projectile drop. It has a blast radius of 3 meters, which outside of 1 meter will not kill the enemy, but only wound them.