Austria First Airmails - 1918 Complete Mint NH Set of 3

In March 1918, Austria inaugurated the world's first regularly scheduled airmail service, delivering wartime mail between Vienna and military headquarters on the Eastern Front in Poland and Kiev. These 3 overprinted stamps, only the second government-issued airmail stamps in the world, paid postage on these dangerous 13-hour wartime flights. Austria #C1-C3