Keep Calm and Carry On Second World War British poster from 1939, estimate $12,000-18,000 at Swann Auction Galleries on August 27.

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However, they were to be used in the event of invasion so were never officially seen by the public. It is believed most were destroyed at the end of the war.

This 1939 example measuring 20 x 15in (51 x 38cm) is one of the smaller formats. It will be offered by Swann Auction Galleries in New York as part of its Vintage Posters sale on August 27 with an estimate of $12,000-18,000.