Issue #81 of Our Army at War (April 1959), the story "The Rock of Easy Co.!" has often been credited by DC as the first appearance of Sgt. Frank Rock.
However, in the Sgt. Rock Archives Vol. 1 (2002), DC included an earlier story from G.I. Combat #68 (January 1959) titled "The Rock!"
And while Sgt. Rock's first recognized story in Our Army at War #81 was called "The Rock of Easy Co.!", DC's Who's Who series from 1985 placed the first appearance of "The Combat-Happy Joes of Easy Co." in Our Army at War #83 (June 1959).