Scapa Flow, flω', a sheltered body of water in Scotland's Orkney Islands. This stretch of sea, about 15 miles (24 km) long and 8 miles (13 km) wide, was a major British naval base in World Wars I and II. After the armistice in 1918 a large part of the German fleet, consisting of 77 surface vessels and 102 submarines, was interned at Scapa Flow by the victorious Allies. In June, 1919, caretaker German crews sank the vessels to prevent them from being divided among the Allied nations. In World War II, a German submarine penetrated British defenses at Scapa Flow in 1939 and sank the battleship Royal Oak.