NYC Timeline: N-400 mailed: 9/10/04 FP: 10/11/04 Interview: 10/07/05 Oath: 10/21/05. 13 months from mailing my N-400, FP, Interview and Oath. Now I am wondering if I could still travel on my birth country's passport (which is still valid for travel) after my Oath next week. Is it legal? Or, am I required by law to get the US Passport if I want to travel out of USA?