Hate to burst the bubble, but as someone who has raised his right hand and been sworn into office as a commissioned officer in the U.S. Army, the verbal oath is simply ceremonial. The real oath occurs with one’s signature on a piece of paper.
Actually, he does have to say it. http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/01/20/MNAF15E20I.DTL