On 4 July 1943 the Polish Prime Minister-in-Exile , General Wladyslaw Sikorski , who was also Commander-in-Chief of the Polish Armed Forces in the West , died in an air crash off Gibraltar as he was returning to England from an inspection tour of Polish forces in the Mediterranean theatre . Until the Germans ' April 1943 discovery of mass graves of 28,000 executed Polish military reserve officers at Katyn , near Smolensk in Russia , Sikorski had wished to work with the Soviets . After Hitler 's invasion of the Soviet Union in June 1941 , the Soviets ' importance to the Western alliance had grown while British support for Polish aspirations had begun to decline . As the war progressed , Polish plans to more completely incorporate Poland 's underground Home Army into the broader strategy of the Western allies — including contingency plans to move Polish Air Force fighter squadrons , and the Polish Parachute Brigade , to Poland — foundered on British and American reluctance to antagonise a vital Soviet ally hostile to Polish autonomy ; on the distance from British-controlled bases to occupied Poland , which lay at the extreme flying range of available aircraft ; and on the frittering away of the Polish Parachute Brigade on a patently flawed British operation at Arnhem , the Netherlands . One of the most important Polish contributions to Allied victory had actually begun in late 1932 , nearly seven years before the outbreak of war when the mathematician-cryptologist Marian Rejewski , with limited aid from French military intelligence , constructed a double of the sight-unseen German Enigma cipher machine used by the German civil and military authorities . Five weeks before the outbreak of war , in late July 1939 , Rejewski and his fellow cryptologists , Henryk Zygalski and Jerzy Rozycki had disclosed to French and British intelligence in Warsaw the techniques and technologies they had developed for " breaking " German Enigma ciphers . Poland 's '' Biuro Szyfrów '' ( Cipher Bureau , operated by the Polish General Staff ) gave the British and French an Enigma double , each . This enabled the British , who had been unable to break German Enigma ciphers at Bletchley Park , to develop their " Ultra " operation . At war 's end , General Dwight Eisenhower characterized Ultra as having been " decisive " to Allied victory . Former Bletchley Park cryptologist Gordon Welchman wrote : " Ultra would never have got off the ground if we had not learned from the Poles , in the nick of time , details both of the German military ... the Enigma machine , and of the operating procedures that were in use by the Germans . " The first Polish military branch to transfer substantial personnel to the United Kingdom was the Polish Navy . Shortly before the outbreak of hostilities , the Polish government ordered three destroyers , for their protection and in anticipation of joint operations with the Royal Navy , to sail for Great Britain . Two submarines also sailed there , the '' Orzeł '' ( Eagle ) arriving unannounced in Scotland after a daring breakout from the Baltic Sea following its illegal internment in Estonia . Polish Navy personnel to come under Royal Navy command comprised 1,400 officers and 4,750 sailors . By chance , Poland 's only two ocean-going commercial liners , MS '' Piłsudski '' and MS '' Batory '' were also on the high seas on 1 September 1939 and were both shortly thereafter requisitioned by the British Admiralty for war service . The former was lost in November 1939 when it struck a mine off the Yorkshire coast . '' Batory '' , however , dubbed " '' the Lucky ship '' " , became a troop and civilian carrier and hospital ship . It effected a major evacuation during the Battle of Narvik and completed hundreds of convoys on the Mediterranean Sea and on the Atlantic , before being surrendered to the control of the communist authorities in Warsaw in 1946
Katyn
Katyn massacre
Poles in the United Kingdom