an all-out assault on the tal b taliban in afghanistan. the new offensive is being called the largest military operation since the start of the war back in 2001. u.s. and afghan forces side by side, hunting down taliban fighters in a battle to seize the terrorist stronghold, the goal to establish security and gain the trust of some 80,000 afghan citizens who are there. we have an exclusive from helmand province. >> reporter: at a firebase in helmand province, the first battalion 6th marine regiment prepares for combat. they've fought in two world wars in iraq and afghanistan. today, it has a new ally on the battlefield.