Two things that have changed since the Vietnam era are communications and the cost of living.

The Socialist Republic of Vietnam.

Language barrier. Nearly all obstacles can be over come...once communications are in effect.

I can't say exactly for Vietnam, but in China they sell at 600 to 800 RMB (about 90 to 110 dollars) for one that actually works, and most markets in Vietnam are selling from the same suppliers as the Chinese markets.

You can get them a lot cheaper, but as soon as you get home you find that only the game in it will work with it and none of the network/communications work.

1. Satellites

2. U-2 spyplanes (fllights over North Vietnam)

3. SR-71 spyplane (Blackbird flights over North Vietnam)

4. Communications monitoring (Desoto Patrols-off the coast of North Vietnam)

5. UAV Firebee (Ryan Unmanned Aerial Vehicle flights over North Vietnam)

6. Spies (Traditional in most wars)