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The Post Office has issued a set of stamps commemorating the British Merchant Navy and the Atlantic and Arctic Convoys of WWII:
First class stamps:
East Indiaman - Atlas, 1813
Royal Mail - Ship Britannia, 1840
Tea Clipper - Cutty Sark, 1870
Overseas letter rate £1.28 stamps:
Cargo Liner - Clan Matheson, 1919
Royal Mail Ship - Queen Elizabeth, 1940
Bulk Carrier - Lord Hinton, 1986
They are still available from local Post Offices or from Post Office Shop online
Larger images here