less palpable. >> check. >> clear. while garcia and tse accomplish their mission, chang's squad is already in the town. how would you say everything is going? >> so far they're doing all right. >> push, push, push! >> go ahead. >> alert. >> even after 16 hours, the battle simulation is far from over. throughout the night, the marines will take turns defending the town. obviously, it's pitch black and we can't use a lot of light because if the enemy sees light, you could be dead. and come down, they'll face their last and biggest test. the final battle with big guns