Prime Minister Sikorski , the most prominent of the Polish exile leaders , was killed in an air crash near Gibraltar on 4 July 1943 . Sikorski was succeeded as head of the Government-in-Exile by Stanisław Mikołajczyk and by Kazimierz Sosnkowski as the top military chief . Sikorski had been willing to work closely with Churchill , including on the issue of cooperation with the Soviets . The prime minister believed that Poland 's strategic and economic weaknesses would be eliminated by a takeover of German East Prussia , Pomerania and Silesia and that Polish territorial concessions in the east were feasible . On the other hand , Sikorski was credited with preventing the Soviet territorial demands from being granted in the Anglo-Soviet Treaty of 1942 . After his death , the Polish government 's position within the Allied coalition deteriorated further and the body splintered into quarreling factions
killed in an air crash
1943 Gibraltar B-24 crash
History of Poland (1939–1945)