GE C4, C6 1922 Pigeon Stamps, Malygun Cancel

VF used. 1922 40, 60 pf. stylized pigeon airmail with Russian icebreaker Malygun cancels. The icebreaker met the Graf Zeppelin in the arctic to transfer mail and canceled postage on cards/letters destined for the Soviet Union. These stamps were outside there period of validity, but were added to letter mail and accepted by the Russians.