Don Blankenship shared this information about this picture:
The first picture (MRF3) is the USS Harnett County sitting just south of the Ben Luc bridge which is also the subject of the other two pictures which you labeled Tan An bridge. This is on the Vam Co Dong river. It's possible I'm mistaken but I feel really sure this is the Ben Luc bridge. It's also quite possible that it may have been referred to as the Tan An bridge because that was the next stop down the highway. The vacant land area to the right of the Harnett County was being dredged and filled at the time I was there for a new Naval Support Activity base at Ben Luc. The little town of Ben Luc sits just north and east of the bridge.