2nd World War - FREE POLISH FORCES IN EXILE IN LONDON. Mourning postcard in tribute to General SIKORSKI, leader of the Free Polish Armed Forces and Prime Minister of the Polish Government in exile since 1939, who died when his plane crashed in Gibraltar on 4 July 1943. RARE AFFRANCHISSEMENT: exile stamps from the 1st issue of 1941, 5 Gr no. 1 ruins of the United States embassy in Warsaw and 25 Gr no. 3 demolition of the Mickiewicz monument in 1940. Obliteration: illustrated commemorative stamp 4-VII-1944.