I know several people that held dual citizenship before joining the military or getting a TS SCI clearance and in all cases they had to officially renounce their citizenship and give up their passports, there were no exceptions. Whether or not the country recognizes your renunciation you can't really do anything about, you have done your part, as long as you never utilize/use that citizenship during your service if it is still in effect. I do know that some countries do not recognize a renunciation and if you finish your service and are under no more obligations to the government, you could get your passport back. Just don't think about doing it while in the service or while holding a TS SCI, it will cause you big trouble. The US does not recognize dual citizenship but it does not really care if you hold citizenship (or a passport) from another country either unless it somehow conflicts with your US citizenship. You renounce your citizenship in other countries if you take the US oath of citizenship but it is not really enforced, as long as there is not a conflict. It is not like some countries however, like Japan, that expressly forbid dual citizenship and will revoke it if you take citizenship in another country. My wife has been treated much better by customs/immigration than me in some cases when we have gone overseas. Other than that, not much.