The American military says it has launched a big attack in Afghanistan against a group called the Taliban, in the south of the country.
It's thought 4,000 Marines as well as 650 Afghan troops are involved.
They are trying to drive the Taliban out before presidential elections in the country this August.
Brigadier General Larry Nicholson said the operation was different from previous ones because of the "massive size of the force" and its speed.
US troops have been in Afghanistan since 2001.
They invaded because they said the Taliban, who were in charge at the time, were sheltering a group called Al Qaeda, who were behind the September 11 attacks on America.
Helmand province, where the new offensive is taking place, is seen as a stronghold of the Taliban.