Obtaining United States citizenship is easier for someone who has served in the military, regardless of whether or not the U.S. was legally in any “hostilities.” When the U.S. is in hostilities, anyone serving can petition for immediate U.S. citizenship, and as an added bonus, the military pays for the filing fees with USCIS. Currently, the U.S. is engaged in legally defined hostilities, and has been since September 11, 2001. That means that anyone who honorably serves in the military right now, even for one day, is eligible. A person can go straight from undocumented immigrant status to citizenship fairly quickly. However, the armed services are not supposed to allow undocumented immigrants to enlist, but immigrants with green cards are allowed to enlist.
For anyone who served in the armed services more than 10 years ago, it is still possible to get citizenship, even if the U.S. was not in hostilities. For service during peacetime, an immigrant needs to have served at least one year and have been honorably discharged. Also, the applicant must have lived in the U.S. for at least 30 months out of the previous five years.
It is possible to get a green card through military service, but it’s fairly rare. To qualify, an applicant must enlist in the U.S. armed services outside the U.S, and their home country’s armed services must recommend them for this immigrant status or they must be a citizen of a country that has a treaty arrangement with the U.S. Only the Philippines, Micronesia, and the Marshall Islands currently have a treaty with the U.S. allowing their citizens this green card status.