Japan intended to built a mother ship for submarines according to the Dutch magazine Marineblad dated 1933 no. 5

An item referred to the magazine Revue Maritime dated July 1933 reporting that Japan intended to built a mother ship for submarines with a displacement of 10.000 (standard) tons and as dimensions 210 x 18 x 5 metres. Her engines were to supply 13.000 hp allowing a speed of 20 knots. To be armed with 12,7 cm guns.