At 12.56 hours on 29 May 1944, U-23 fired a spread of two torpedoes at tanker of about 1800 tons, which was in tow escorted by two warships and aircraft. Wahlen heard two detonations, but could not observe the effects because the U-boat was attacked with depth charges for the next two hours. In fact the tug Smelyj was hit by one torpedo and sank off Babushery near Suchumi.