Poland was the first country to stand up to Germany in 1939, and maintained an underground army during the years of World War II. The underground army was organized in occupied Poland in October 1939 and worked until April 1945, when it helped to establish a legitimate authority in post-war Poland while liberating territory with the aid of Polish Forces from the west. This military history covers the attempts of General Wladyslaw Sikorski and his successor (General Kazimierz Sosnkowski) to integrate the Polish forces into Western Strategy, and trying to have their clandestine forces (the Armia Krajowa) declared an allied combatant and legitimized by the Western powers before the eyes of both Germans and Soviets who sought Poland's destruction. The work opens with some general remarks on the inter-war period of 1919-1939, and then concentrates on the period of October 1939 through January 1945 and V-E Day. It covers such topics as Poland's part in the Norwegian and French Campaigns, the Battle of Britain, Polish Intelligence Services, Military Radio Network, Feluccas, the creation of the Polish Parachute Brigade, the German invasion of the Soviet Union, the Bomber Offensive, the Katyn graves, Polish air crews in RAF transport command, Tehran, Polish Wings in the 2nd Tactical Air Force, the Bardsea Plan, the invasion of Normandy, the Pierwsza Pancera, the Warsaw Uprising, Operation Freston, the disbanding of the Polish Home Army, and Yalta. A conclusion and several appendices (including a chronology, costs of the Polish forces based in the UK, list of Polish squadrons in UK, and the texts of Polish-British agreements) close the work.