 The use of icebreakers and, later, aircraft as platforms for scientific work were developed.In 1929 and 1930 the Icebreaker Sedov carried groups of scientists to Severnaya Zemlya, the last major piece of unsurveyed territory in the Soviet Arctic; the archipelago was completely mapped under Georgy Ushakov between 1930 and 1932.Particularly worth noting are three cruises of the Icebreaker "Sadko", which went farther north than most; in 1935 and 1936 the last unexplored areas in the northern Kara Sea were examined and small and elusive Ushakov Island was discovered.