Answer
Leningrad. Voroshilov was in command of the Leningrad Military District and the city of Leningrad when the Germans invaded the Soviet Union in June 1941. Despite the city's extensive fortifications and the presence of a large number of troops, Voroshilov failed to prevent the Germans from encircling the city in September 1941. This failure led to a lengthy and costly siege of Leningrad that lasted until January 1944.