This is A2C John Cantrell working tower Alpha-15.  I was training him in early 1967.  I left 1 April 1967. At the time, the requirements for the two special towers were: 1.  20/10 eyesight. 2.  Recommended by the other observers, there were only six at the time.  (2 Regulars, 2 Backup and 2 in training.) 3.  1 week map reading course that was taught by US Army personnel.  This was to learn grids and azimuths. 4.  OJT in a tower by regular tower observer. John may have been in Alpha-15 when the TET Offensive of 1968 started.  I don't remember what his DEROS was.