Russia C26-29 Imperf Graf Zeppelin Arctic Flight - Scarce 1931 Russia Complete Imperforate Mint Never-Hinged Set of 4

In July 1931 the Graf Zeppelin carried an international team of scientists, including polar explorer Lincoln Ellsworth, to the North Pole to conduct experiments and map the Arctic. To mark this historic flight, the Zeppelin carried a sack of souvenir covers that would be exchanged with the Soviet icebreaker Malygin. This interesting set shows the Zeppelin exchanging mail with the Malygin, with a polar bear curiously looking on (Russia #C26-29)