The Vietcong were masters of what is known as guerrilla warfare or guerrilla tactics during the conflict in Vietnam. 

They could blend in with and move through the local terrain much better than U.S. forces. Most of the Vietcong were young, impressionable teens. At first timid, they were given political instruction and training to increase their level of commitment and confidence. To further their advantage, they used these guerrilla tactics. Rather than large, drawn out battles, they utilized ambushes and traveled through a system of hidden tunnels. The tunnels connected huge networks of store rooms, quarters, kitchens and even hospital type care areas. Landmines, boobytraps and the element of surprise further helped the Vietcong succeed. 

The Vietcong became highly successful at stealing U.S. weaponry and eventually amassed a huge store of stolen weapons, using their own weapons against the U.S. forces. 

The Vietcong ‘s tactics were successful more for strategic reasons than for actual tactical reasons.

Tactics have to do with the small-scale issues of who wins a particular battle.  The Vietcong’s tactics were mainly guerrilla tactics.  They would not engage in pitched battles with the Americans but would instead do “hit and run” attacks.  This would not typically result in major tactical victories for the Vietcong.

What the tactics did do was to wear down the Americans’ resolve.  This is a more strategic issue.  Strategy is about the big picture of who is winning a campaign or an entire war.  Because the Vietcong engaged in these guerrilla tactics, they denied the US the ability to win a crushing victory.  Instead, they forced the US to be patient and to stay in the war for the long haul.  By doing this, the Vietcong eventually made the US give up on the war.  In this way, the tactics used by the Vietcong were good strategy even if they did not win a great number of tactical victories.