After you hold off the first attack from the Viet Cong, your next objective instructs you to go back to the starting point of the mission to defend another attack from the VCs. When you reach the open area where your squad started, look to the left. You should see a mortar launcher ready to use. Have Ragman and either Doc or Hoss use it. It requires two people to use (one fires and the other aims). Start shooting towards the openings that VCs come from and start firing. You may not seem to hit anything, but should notice that less VCs come from the entrances once you start firing. Keep this up until the mission ends or the mortar gets destroyed. Note: The mortar does not have unlimited ammunition; use it wisely.