500 Ðồng

The National Bank of Vietnam turned to Thomas De La Rue for this series at a point when South Vietnam's currency was under sustained pressure — not from counterfeiting alone, but from a parallel economy running on U.S. military payment certificates and black-market dollars that made the đồng increasingly marginal in daily high-value transactions.

De La Rue's London production gave the note stronger security credentials than the locally printed issues of the same period, though the single watermark remained modest protection by the standards of the day.