September 30, U-boat losses on this day amounted to five between the two wars. Four out of the five sank for unknown reasons.
1915: U-26 lost in the Gulf of Finland (30)
1917: UC-21 Departed Zeebrugge and never heard from again. (27)
1918: U-102 (42) and UB-127 (34) Both presumed to have been mined.
1944: U-863 (69) Sunk in the South Atlantic by depth charges from US aircraft.
In total 202 U-boat men were killed.