"Ro-38" got underway from Truk on 20 January 1944 with the commander of Submarine Division 34 aboard to begin her first war patrol, assigned a patrol area in the Caroline Islands in the vicinity of Woleai. On 22 January 1944, she received orders to rescue Imperial Japanese Navy Air Service aircrews of the 531st Naval Air Group at Woleai and the 755th Naval Air Group at Maloelap. With U.S. ships gathering for the invasion of the Marshall Islands, "Ro-39" was ordered on 30 January 1944 to move to a patrol area northeast of Wotje.