[3] Assigned to the III Flotilla, U-46 began her first war patrol on 29 March 1916.

Remaining in the III Flotilla for the rest of the war, she conducted a total of 11 war patrols before the war ended on 11 November 1918 and was credited with sinking 51 merchant ships totaling 138,942 gross register tons and one auxiliary warship of 1,372 gross register tons and damaging one merchant ship of 7,378 gross register tons.

[3] Transferred to Japan after surrendering, the submarine was commissioned into the Imperial Japanese Navy in 1920 as O-2.

[3] A photo of U-46 apparently at the time of transfer to Japan shows the submarine docked and flying the flag of the Imperial Japanese Navy over the flag of the Imperial German Navy.

[7][8] Other sources claim that in 1925, O-2 was rebuilt at Yokosuka Naval Arsenal to serve as a testbed for submarine salvage operations by the submarine salvage ship Asahi and foundered in the Pacific Ocean in a storm off the coast of Japan during her transfer voyage from Yokosuka to Kure on 21 April 1925,[3] adding that an American merchant ship sighted her derelict hulk floating in the Pacific west of Oahu, Hawaii, on 5 August 1927, and that the hulk subsequently was scuttled.