In the early 1990s, roughly 1.5 million documents on microfilm were transferred from the Hoover Institution to the Polish National Archives. These documents, the records of the Polish government-in-exile, had originally been entrusted to the Hoover Institution following World War II and the subjugation of Poland by the Soviet Union.
See my article on Jan Karski for more information about how these collections were obtained. My other article in Polish on Karski and the Hoover Institution is available here (pg. 153).
In 2011, the microfilmed documents were digitized and uploaded to the internet, and are now accessible to anyone in the world. Though four years have passed, many historians and others interested in Polish history during World War II, don’t know about the availability of these materials.
In the video below I explain how to search the szukajwarchiwach.pl website, where the documents are hosted, in conjunction with the Online Archive of California (OAC), where the finding aid descriptions of the contents of these collections are available.
If you have any questions or issues with this process, leave a comment below the video on this page or on YouTube.