It may surprise you to know that in the enlisted ranks (non-officers) we swore to obey the orders of officers appointed above us.Enlisted service members also take the oath at the beginning of each term of enlistment. Officers take the oath only once at commissioning.
WWG1WGA
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
Twice - once when commencing induction into training and once upon commissioning. So enter USNA at beginning of plebe summer oath - graduate oath. Enter OCS oath commission oath. ROTC start oath commission oath.
Mustangs are different as they are already under their enlistment oath but not sure the exact details on when the first take their officers oath.