Maizuru Naval Arsenal
On 25 August 1941, "Ōi" returned to Maizuru Naval Arsenal for conversion to a torpedo cruiser with 10 quadruple mount torpedo launchers (a total of 40 tubes), housing long-range oxygen-propelled Type 93 "Long Lance" torpedoes arranged in two broadside rows of five, i.e. 20 per side. Modifications were completed on 30 September, and "Ōi" was assigned to the CruDiv 9 of the IJN 1st Fleet together with her sister ship .