 On 14 May, Wernicke was succeeded by Kapitänleutnant Kurt Schwarz as commander of UB-42. The 27-year-old Schwarz, who had previously commanded the Type UB I boat UB-14, led UB-42 to sink her largest ship, Cestrian, on 24 June. The 8,912-ton former Leyland Line steamer was in use as a troopship, carrying 800 troops and horses when Schwarz sent her down 4 nautical miles (7.4 km; 4.6 mi) southeast of Skyros in the Aegean. Three of Cestrian's crewmen died in the attack and, according to R. H. Gibson and Maurice Prendergast, "splendid discipline" among the embarked troops was the sole reason that none were lost.
