I am retired, living in Australia and a Vietnam veterans. I am still a citizen of the United States. I receive some social security payments in conjunction with the aged pension from Australia. I understand that former military are eligible for payments due to their service but because I’m outside of the US do not know how to contact nor where to send my copy of the DD 214.
If all of your active military service was after 1967, then Social Security wouldn't need to see proof of your active duty and your benefit rate should include all of the proper credits for your service. If you had active
duty prior to 1968, though, then you may need to submit proof of your service in order to receive the proper credits (https://www.ssa.gov/OP_Home/handbook/handbook.09/handbook-0953.html).
If you had service prior to 1968 and didn't previously submit proof of your service at the time you filed for Social Security benefits, you could mail a copy of your form DD-214 to any U.S. Social Security office along with a request for recalculation of your benefit rate. Or, you may be able to submit the form to a Social Security office in Australia and ask them to forward it on to the U.S. Social Security Administration. For more information on addresses, refer to the last part of this Social Security reference: https://www.ssa.gov/international/Agreement_Pamphlets/austrlia.html.