As funny as it may sound it was very possible to "volunteer" for the draft. I know. I did it.
For most young men at the time you registered for the draft at 18, got your draft card, and waited.
Or you went to college (or some other qualifying school) and got a 2S deferment.
Or you visited your friendly recruiter and volunteered.
Or you called your local draft board, as I did, and asked them to send you a draft notice. I had mine in a matter of days and two weeks later was a "US" with a two year commitment like all the other draftees (unlike volunteers who were RAs with 3 and 4 year obligations).
you make me curious now .... what year was that?
I've tried to tell 'em Colonel. What did you do during that two years to switch over?
As funny as it may sound it was very possible to "volunteer" for the draft. I know. I did it.
I did it too, as did someone else I knew. The only thing different was that I was in college and I had a student deferment, so I had to go in to my Draft Board and sign a "Waiver of Deferment". Then, with the deferment signed, I simply became another 19 year old with no deferment. I asked them to induct me ASAP (I was afraid the war would be over before I got there [who knew?], but they made me wait 2 months). I was inducted. My serial number started with "US", I had no MOS choices, and I did two years. No one, other than the Draft Board knew, unless I told them.