from Humans Are Free:
Nazi Party Secretary Martin Bormann was at the heart of the Nazi apparatus. He signed Hitler’s paycheck. Louis Kilzer examined the wire traffic between the spy known as “Werther” and Moscow and determined that only Bormann had access to this information.
The Soviets were able to ask very detailed questions about Nazi defenses and intentions. The result was the decisive Nazis defeats at Stalingrad and Kursk. Louis Kilzer writes, “Bormann had been as useful to Russia as fifty Red Army divisions.”