1940 Gryazovets (Vologda region) registered letter from Tarnów sent 15.11.40 purple stamp in box "ПОЧТОВЫЙ ЯЩИК No 11". - post office box - secret address of Gryazovets. The camp in Griazovets housed those rescued from the Katyn massacre or ex-interned from the Baltic States, German censorship on the envelope and a stamp from Moscow, where letters sent to imprisoned Poles were sent to secret post boxes.
Letters written to interned Poles are particularly rare, as they had to accompany the soldier throughout the war.