Tunnel Vision is the fourteenth chapter of Uncharted 2: Among Thieves.
Nathan continues his trip forward through the train, fighting more mercenaries, and facing off against Draza for the phurba dagger, before being shot by Flynn. Badly injured, he runs and sets off an explosion that causes several carriages of the train to derail and crash down a cliff, with himself inside.
The mercenaries you fight are mostly the same as all the others you would've fought on the train. At some point you'll come across a Heavy Weapons Trooper. The Heavy Weapons Troop will climb onto a train car carrying logs, which is held together with some big couplings. Shoot the couplings to dislodge the logs and kill the soldier.
Before going on to face Draza, you will take control of an anti-aircraft gun to destroy the helicopter.
You will face Lieutenant Draza in a train car which is mostly symmetrical, giving a lot of cover. Draza will stand at the opposite end of the train car and shoot at you with an M4. Just keep shooting back and whittle his health down. Every now and again he'll throw a grenade at you, which you'll have to avoid; when this happens exit cover and run up and start meleeing Draza. Once you've finished meleeing him, Drake will push Draza back down to the opposite end of the train car. At this point, just take cover again and resume shooting.
Behind the scenes
"Drake's on a Train" was the original title for this chapter. As with all chapter titles, it was thought of by lead game designer Richard Lemarchand. However, the title had to be changed to "Tunnel Vision" for the full release of the game. The story behind the title of the chapter was first revealed by Naughty Dog at PAX East 2010.