This a securty police armored vehicle on the base perimeter at night. The week before I arrived at Phan Rang sappers tried to come in through the perimeter. They never made it and were all killed. I actually started my time in Vietnam at Phan Rang Air Base. There was not much to do and I got bored real fast so I started going out at night and hanging out with the Secutiry Police guys on the perimeter. Luckily this turned into a few photos which got some attention in Saigon causing my later assignment there.