After Christmas leave in England in 1943, Jacob and Iris sailed to the Soviet Union in January 1944 on board a ship of the Arctic Convoy. They spent the remainder of the war in Moscow, covering the advances of the Red Army in Odessa, the Crimea, and through Vitebsk, Minsk, Poland, and on to the fall of Berlin. He published "A Window in Moscow" in 1945. His experiences made him sympathetic towards the Soviet regime and he stayed in the Soviet Union, on and off, until the start of the cold war in late 1947. Iris had become a Communist and her ideas strongly influenced him. He suspected that her membership of the Communist Party worked against him even when they were separated.