The Ōtomari (大泊)[1] was an icebreaker of the Imperial Japanese Navy (IJN) serving during the 1920s through World War II, the only ship of her class.

The Imperial Japanese Navy was not able to dispatch their warship to Nikolayevsk-on-Amur which froze, because they did not have an icebreaker.

The IJN hurried the construction of Otomari, because they wanted her by the Winter of 1921, and she was launched less than four months after her keel was laid down.

She was assigned to Ōminato Guard District and took northern patrol duties, and continued active service throughout her life.

Because Ōtomari was small and aging by World War II, the IJN planned her succeeding ship Esan (恵山, Project Number J23, 6,800 tons standard) under the Kai-Maru 5 program in 1942; however Esan was canceled in 1943.