Rats tend to congregate wherever there are large amounts of people living close together in a small amount of space, particularly when there is a high death rate amongst those people. The city of Leningrad was truly at war, and not just with they army outside but with hunger and rodents inside as well. They rats were a real danger to people, not only did they devour what little food people had stored they also carried diseases that often proved fatal.
Then the Russian government had a great idea. The solution was obvious. Cats. Five thousand cats were gathered from surrounding cities and ant set lose in the beleaguered metropolis. The rats didn't stand a chance. Even now there are many older residents who can recall owning one of the siege heroes after the crisis had passed. There's only one question remaining:
If the government was able to get five thousand cats into the city why couldn't they just send more food?