Maizuru Naval District
Upon commissioning, "Ro-33" was attached to the Maizuru Naval District. On 31 May 1937 she was reassigned to Submarine Division 21 in the Sasebo Naval District. On 9 April 1938 she got underway from Sasebo, Japan, for a training cruise in southern Chinese waters that concluded with her arrival at Kīrun, Formosa, on 14 April 1938. Submarine Division 21 was reassigned to the Combined Fleet on 15 December 1938 and to Submarine Squadron 2 in the 2nd Fleet on 8 April 1939. "Ro-33" was placed in the Second Reserve in the Sasebo Naval District on 15 November 1939.