I graduated from high school in 1968. The Vietnam War was featured every night on the news. War protests were happening all over the country including at some local colleges in Southern California. I went to some of those protests more as an observer than as a participant. The war machine was actively sweeping up boys 18 and older to serve in the military. My plans did not include the military and the one way to avoid the war was to go to college with a 2-S deferment.
All of the boys registered with the Selective Service at age 18 and received a classification. The classifications ranged from 1-A, fully elegible, to 4-F, physically unfit. 2-S was somewhere in the middle and indicated that you were a student and as long as you maintained that status you were 'safe'.
Sometimes your best made plans change.
'Greetings' from the President of the United States