<P> The Norwegian merchant fleet, then the fourth largest in the world, was organized into Nortraship to support the Allied cause . Nortraship was the world's largest shipping company, and at its height operated more than 1000 ships . </P> <P> Norway was neutral when Germany invaded, and it is not clear when Norway became an Allied country . Great Britain, France and Polish forces in exile supported Norwegian forces against the invaders but without a specific agreement . Norway's cabinet signed a military agreement with Britain on 28 May 1941 . This agreement allowed all Norwegian forces in exile to operate under UK command . Norwegian troops in exile should primarily be prepared for the liberation of Norway, but could also be used to defend Britain . </P> <P> The invasion of Poland on 1 September 1939, started the war in Europe, and the United Kingdom and France declared war on Germany on 3 September . Poland fielded the third biggest army among the European Allies, after the Soviet Union and United Kingdom, but before France . The country never officially surrendered to the Third Reich, nor to the Soviet Union, primarily because neither of the totalitarian powers requested an official surrender, and continued the war effort under the Polish government in exile . However, the Soviet Union unilaterally considered the flight to Romania of President Ignacy Mościcki and Marshal Edward Rydz - Śmigły on 17 September as an evidence of debellatio causing the extinction of Polish State, and consequently declared itself allowed to invade (according to Soviet position: "to protect") Eastern Poland starting from the same day . It must be noted that the Red Army had invaded the Second Polish Republic several hours before Polish president fled to Romania . The Soviets invaded on 17 September at 3 a.m., l while president Mościcki crossed the Polish - Romanian border at 21: 45 on the same day . The Polish military continued to fight, and the last major battle of the war, the battle of Kock, ended at 1 a.m. on 6 October 1939 with the Independent Operational Group "Polesie," a field army, surrendering due to lack of ammunition . </P> <P> Polish soldiers fought under their own flag but under the command of the British military . They were major contributors to the allies in the theatre of war west of Germany and in the theatre of war east of Germany, with the Soviet Union . The Polish armed forces in the West created after the fall of Poland played minor roles in the Battle of France, and important ones in the Italian and North African Campaigns . The Polish People's Army took part in the Battle of Berlin, the closing battle of the European theater of war . They occupied the city alongside the Soviet Red Army . </P>

When did the soviet union join the allies