Caleb IV was a Federation outpost near the Klingon border.
In the 2260s, it was attacked by two Klingon divisions led by Kang and Kor. Aboard the D5 class cruiser IKS Klothos, Kor outmaneuvered the defending Federation forces by attacking with an initial feint, and then returning with his full force, catching the Federation in the midst of their repair work.
A century later, during a similar attack on a Dominion base at Trelka V, Kor believed that he was back at Caleb IV. (DS9: "Once More Unto the Breach")