A popular strategy is to run around in circles in a large area until all of the zombies are behind you, then shoot what ever bullets you have into the horde. When you run out of ammo, switch to a thundergun, or a ray gun to clear the horde.

The Military Assistance Command, Vietnam  Studies and Observations Group (MACV-SOG) was a highly classified, specialized unit that operated during the Vietnam War. It conducted covert operations, reconnaissance, and unconventional warfare missions behind enemy lines.