Lieutenant John Martin was the CO of the soldiers defending in the trenches. Nate later found him and another soldier with a infected VC soldier tied to a stretcher, thinking he was rabid. He and the other soldier climbed out of the trench with the VC. As Nate progressed through the trenches Lt. Martin jumped into the trench yelling that the VC was crazy and ran off. He is later seen on at the end of the level. He's seen on a River Patrol Boat as the driver.
In the next level a wounded man they had with them became an infected and started to attack them. Martin shoots the soldier a couple times but he pulls the gun away from him and pushes him overboard and jumps after him.