Tsutomu Sakuma (佐久間 勉, Sakuma Tsutomu; September 13, 1879 – April 15, 1910) was a career naval officer in the Imperial Japanese Navy, and a pioneer submarine commander, known primarily as the commanding officer during the sinking of Submarine No.6.
Source: “Tsutomu Sakuma”, English Wikipedia (CC BY-SA 4.0), excerpt