United States. Department of the Treasury. "U.S. Savings Bonds Issued and Redeemed Through December 31, 1968," in United States. Department of the Treasury. "Volume 163," Press Releases of the United States Department of the Treasury (October 1, 1968 - January 20, 1969) : 591-592. https://fraser.stlouisfed.org/title/6111/item/587006/toc/541284 , accessed on June 23, 2024.