Late 60's actually, they were a late edition to the Case line up. The pattern is much earlier very early 1900's, perhaps last quarter of the 1800's, they were being made in Germany. The German name for the pattern roughly translates to "folding butcher Knife" or similar in older catalogs.
Post WWII, Henckels, Herder, and Schlieper (Eye Brand) models both standard and jumbo sized were getting really popular in the United States, I'd bet that caused Case to introduce it. Ka-Bar also introduced a jumbo version before Case too.