She joined Vice Admiral Marc Mitscher's Fast Carrier Task Force at Pearl Harbor in January 1944 and served as an important part of that mighty force for the remainder of the war. Her rapid-fire guns protected the carriers against aerial attack. "San Diego" participated in "Operation Flintlock", the capture of Majuro and Kwajalein, and "Catchpole", the invasion of Eniwetok, in the Marshall Islands from 31 January to 4 March. During this period, Task Force 58 (TF 58) delivered a devastating attack against Truk, the Japanese naval base known as the "Gibraltar of the Pacific."