(a) Permanent ineligibility Notwithstanding the provisions of section 405(b) (!1) but subject to subsection (c) of this section, any alien who applies or has applied for exemption or discharge from training or service in the Armed Forces or in the National Security Training Corps of the United States on the ground that he is an alien, and is or was relieved or discharged from such training or service on such ground, shall be permanently ineligible to become a citizen of the United States. (b) Conclusiveness of records The records of the Selective Service System or of the Department of Defense shall be conclusive as to whether an alien was relieved or discharged from such liability for training or service because he was an alien. (c) Service in armed forces of foreign country An alien shall not be ineligible for citizenship under this section or otherwise because of an exemption from training or service in the Armed Forces of the United States pursuant to the exercise of rights under a treaty, if before the time of the exercise of such rights the alien served in the Armed Forces of a foreign country of which the alien was a national.