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.
On April 15, 1910, while engaged in a practice dive in the Inland Sea off of the coast of Yamaguchi Prefecture, the submarine suffered a malfunction resulting in the loss of the ship and crew. Two days later the submarine was recovered by Japanese authorities, and Sakuma's journal was found, with a detailed analysis of what may have caused the accident, ending with an apology to Emperor Meiji for the loss of the submarine and 14 crew members before the ship's air ran out. The journal was posted in later press reports, and Sakuma became a posthumous national hero and an example for courage and steadfastness within the Imperial Japanese Navy.
