This is a 1969 US Army Military Register. Does anyone know what the "Basic Branch" designation of "AN" stands for"
Okay, I think I found the answer, according to a Wiki article, (AN) would be Nurse Corps https://en.wikipedia.org/wiki/List_of_United_States_Army_careers
If the initials themselves match those used (in the past) in England, the simple answer is "Auxiliary Nurse".
However, I just checked at https://www.google.co.uk/search?q=ancillary+or+auxiliary+nurse&sca_esv=563983722&ei=CGP8ZMSPJ7u2hbIP3eqL-Ac&ved=0ahUKEwjEs4rxwZ2BAxU7W0EAHV31An8Q4dUDCBA&uact=5&oq=ancillary+or+auxiliary+nurse&gs_lp=Egxnd3Mtd2l6LXNlcnAiHGFuY2lsbGFyeSBvciBhdXhpbGlhcnkgbnVyc2UyBRAhGKABSLCzA1CWD1iElANwAXgBkAEAmAFnoAGXC6oBBDE5LjK4AQPIAQD4AQHCAgoQABhHGNYEGLADwgIKEAAYigUYsAMYQ8ICBxAAGA0YgATCAgYQABgeGA3CAgoQIRigARjDBBgKwgIFEAAYogTiAwQYACBB4gMFEgExIECIBgGQBgo&sclient=gws-wiz-serp and maybe they represent "Ancillary Nurse".
Will leave you to decide whether either, or neither, in this specific example!