World War I would be the first time that a major Marine unit operated seperately from the Navy. They transformed from an anti-guerilla force used to fight in the Banana Wars to a large conventional force needed to fight the Central Powers. The Marines fielded two brigades, the 4th Brigade and the 5th Brigade, although the 5th arrived too late to see any combat. The 4th Brigade was assigned to the Army's 2nd Infantry Division and served with distinction until the armistice.