 "U-73", "U-81", "U-458", "U-565", "U-593", "U-595", "U-605" and "U-617" assembled around Oran as "Gruppe Delphin" (Group Dolphin); "U-77", "U-205", "U-331", "U-431", "U-561" and "U-660" assembled around Algiers as "Gruppe Hai" (Group Shark).Five U-boats were sunk opposing the invasion.Allied armies advancing through North Africa and Sicily constructed a system of airfields increasing the frequency of U-boat detection by aircraft.