Fitzroy Maclean, then a young diplomat in the British Embassy, states in his memoir Eastern Approaches that Herwarth condemned the appeasement of the Munich Agreement, predicted a Soviet–German commitment to non-aggression (which came to pass as the Molotov–Ribbentrop Pact), and saw ahead to what he called "the destruction of Germany".

In his memoirs (Witness to History, 1973), former U.S. ambassador to Germany Charles E. Bohlen reveals how, on the morning of 24 August 1939, he visited Herwarth at the German embassy and received the full content of the secret protocol to the Molotov–Ribbentrop Pact, signed the day before.

[1] According to the website of the German embassy in London,[2] Herwarth and his superior, Ambassador von der Schulenburg, had already been trying since before the Munich Agreement to persuade Britain, France and the United States not to give in to Hitler's territorial demands.

Von Herwarth is also held to be one of the German officials who informed the Allies on the decision to launch Operation Barbarossa in 1941, and to have given some of the earliest accounts of atrocities against Jews[3] and other civilians behind the Eastern Front and in the Holocaust.

Vulfsons was the first person in the USSR to publicly confirm the authenticity of the secret protocols to the German-Soviet pact of 1939 dividing Eastern Europe into "spheres of influence", a copy of which he obtained in the archives of the German Foreign Office.