1940 Pavlishchev Bor - mailbox number 11/P-43 in Moscow, a card from Pavlishchev Bor internment camp sent to Sokolka, the letter went via Moscow - date stamp dated 19.11.40, Lithuanian form with receiving stamp from Sokolka, which was under Soviet occupation at the time. The camp in Pavlishchev Bor housed those rescued from the Katyn massacre or ex-interns from the Baltic states, hence the Lithuanian card form.
Great rarity.