That's covered under the provisions of the UCMJ.
I took my oath 46 years ago this month. It hasn't expired, yet.
I've mentioned it here before, but have a look at www.oathkeepers.org
Crusader
Oh..I know it is covered in the UCMJ....and upheld, but few troops peruse it.
It just needs to be in the oath so each soldier hears it at the start of his service.
Took my oath on June 21st of 65 when I was 18. The biggest and most important commitment of my life to then..and still way up there. I remember thinking I was carrying on the 'tradition'.