I have found this website to be very informative and good reading . There is one thing I am unsure about and that is what exactly the Hat Dich Secret Zone is and why a part of the geographical area in the Phuoc Tuy Province gained that name . Thanks in advance for any assistance.

If you have a look at the article "Anatomy of a Bunker Contact ..." the Hat Dich is described in paragraph 2 and is partly shown in Map 1. It is in the top north-eastern third of that map and straddles the three province borders. Nui Dat was about 15 clicks to the south east.