The evacuation of some part of the Polish army and the civil authorities did not cease the society’s resistance to the occupiers. Following the end of the invasion of Poland, the structures of the Polish Underground State started to be established. They were based on the soldiers of the Polish Army who remained in the country. The vast majority of the Polish conspiracy was subject to the legal Polish government, which had been established in the Great Britain. Acting in consultation with His Majesty’s government, they sent to the country weapons, instructors and money necessary to fight the enemies.

The Home Army (Polish: AK), the biggest and the most well-known formation of the Polish Underground State, was established on 14th February 1942 upon the order of Commander-in-Chief Gen. Władysław Sikorski. Except for armed resistance, its main tasks included also: propaganda, intelligence, communication etc. The unit responsible for the sabotage actions was Kedyw (Polish: Kierownictwo Dywersji Komendy Głównej AK) – Directorate of Diversion of the Home Army Headquarters.

Home Army’s activities included among others: training of the conspiracy units members, motivating society to fight and resistance, performing information actions, gathering/ collecting weapons. Well-developed intelligence passed important information to the western allies e.g. concerning the location of weapons factories. Sabotage campaign were conducted – supply lines were cut off/broken, the emblem of the fight with the occupier (an anchor) was painted or sticked, German dignitaries and those collaborating with the enemy were liquidated.
The culminating point od the Home’s Army activity was the action “Storm” (1944–1945) and the Warsaw uprising (1st August 1944). Due to Soviets’ behaviour i.e. disarming, arresting and murdering the Polish underground officers and soldiers, as well as the failure of the Warsaw uprising, the Home Army was dissolved in January 1945.
But the conspiracy structures and the will to fight remained.