The U.SA had KHE SANH; HUE etc to worry about and fear. For us ANY mention of the Cambodian border terrorised us. We would have an OG  [Orders Group], prior to an operation and there was an almost audible gasp from the N.C.O.'s; when we were told it was the "Cambode" border area. This; put quite simply is where the HO CHI MINH Trail;[ which meandered all the way from North Vietnam] entered South Vietnam. Along it poured tens of thousands of N.V.A. Regulars and with them came some of the most sophisticated weapons and explosives. Their direct mission was to hit Saigon; an example of this infiltration was the Tet Offensive in early 1968. The "Cambode Border" was sheer hell and we dreaded the place.The looks on the soldiers faces as we waited on Luscombe field , for the choppers, told the story; they did not expect to come back.The Regular Army [N.V.A.], were FAR more dangerous than the farmhouse variety Viet Cong. They were an ARMY and they fought like an ARMY. [well disciplined; prepared to do "anything" to win. At one time; I was the bodyguard to the Australian AMBASSADOR and hundreds of them hit the compound and then ran down the road towards Saigon; where they died when they ran into a ambush of U.S.A. helicopter gunships.  The Cambodian border was riddled with very well hidden bunker systems; often linked by tunnell systems. It was a place of sheer death. When they attacked ; they would signal the direction of assault with a hail of tracer fire.