Wilhelm Kiesewetter born 28 Oct 1878 in Leipzig . He was a reserve officer and likely saw service as master or as an officer on a (larger) merchant ship.
Kiesewetter was assigned to SMS Zieten when the war began. Zieten was an old aviso/sloop that was used as a patrol vessel during the war. Kiesewetter first seems to have been on U-boats in about May 1915, as an officer on U 44 on the newly commissioned U 44 and then U 2 and U 1 at the U-Boat school. By September 1915, he was assigned to U 45. He would remain with that boat until assuming command of UC 56 in February 1917. UC 56 was at the time assigned to Baltic flotilla (small “f”, not the units exact name) operating against Russia.
UC 56 wasn’t very active while in the Baltic except during Operation Albion: https://en.wikipedia.org/wiki/Operation_Albion
The U-boats assigned to the Baltic then got transferred to Flanders. UC 56 arrived in Zeebrugge on January 3, 1918. and then did an operational work-up patrol along the English East Coast from Jan. 5 to 22, 1918. (SOP for new boats/commanders to Flanders.)
UC 56’s first patrol through Dover was from February 13 to March 2, 1918 on which Kiesewetter sank the Glenart Castle.
UC 56’s patrol after that, again through Dover to the Irish Sea, was from March 23 to April 6, 1918.
UC 56’s final patrol was from May 13 to May 24, ending with UC 56’s internment at Santander with mechanical problems.
Kiesewetter was repatriated via Falmouth where he was arrested with the intention of prosecuting him for a war crime, but he had been issued with a safe conduct by a foreign diplomatic service and after two weeks of deliberation the authorities decided that the dafe conduct had to be honoured and he was released. He survived to rejoin the U Boat service in 1939 where he was the oldest submarine captain in the world, commanding a training vessel UC-1 at the age of 62.
February 26, 1918
3 o’clock of the morning
Wind – West 2 Sea State 2 Westerly swell Visibility – very good
On port side a passenger steamship was sighted that had (mis-)placed lights – the side lights were swapped over, definitely in order to confuse the onlooker as to which course it was taking. Steam ship is heading on the 230 degree course. We engage in the presetting maneuvre in order to attack from underwater.
Fired from (torpedo) tube 1. G… torpedo. Hit at the stern. Straight afterwards a second detonation. Steam ship was heavily loaded, definitely had munition on board.(My italics) 150 in length. Size 7000 tons. To the stern end the passenger deck was [protected?]. The steam ship sank after 5 minutes.