Maizuru Naval Arsenal
"Ro-33" and her sister ship were placed in Third Reserve at Sasebo, Japan, on 15 May 1941, and while in reserve "Ro-33" relieved "Ro-34" as flagship of Submarine Division 21 on 21 May 1941. From mid-October through early November 1941 she underwent repairs and a refit at Maizuru Naval Arsenal in Maizuru, Japan. After the work was complete, she returned to active service, probably in mid-November 1941.