"Harrison" sailed with the Southern Attack Force 22 January, and arrived off Kwajalein 31 January. She screened battleships and while the larger ships pounded shore installations, and sank a small tanker with her guns as the Japanese ship attempted to escape from the lagoon. As the Marines landed on Kwajalein and advanced over the numerous islands in the atoll, "Harrison" entered the lagoon 4 February and rendered close fire support. She spent the next 4 weeks patrolling offshore and anchored in the lagoon, departing 1 March for Efate, New Hebrides.