United States. Department of the Treasury. "U.S. Savings Bonds Issued and Redeemed Through April 30, 1967, May 8, 1967," in United States. Department of the Treasury. "Volume 157," Press Releases of the United States Department of the Treasury (March 1, 1967 - May 31, 1967) : 4-6. https://fraser.stlouisfed.org/title/6111/item/587000/toc/540505 , accessed on June 2, 2024.