Between 20.17 and 21.12 hours on 24 August 1943, U-23 fought a gun battle against the former pilot boat/hydrographical vessel Shkval off Cape Kodor, 22 miles south of Sukhumi. The U-boat tried to ram the vessel and also used hand grenades and explosive charges. The minesweeper completely burned out and sank at 23.15 hours. Three crew members were lost. Seven others abandoned ship in a lifeboat and reached the coast at 11.00 hours the next day.