The Red Army found itself confronting two enemies in 1942. One of them was the German Wehrmacht, which during its retreat from Stalingrad was ravaging the Red Army; the other was an invisible enemy that was causing a growing number of casualties. Cholera was spreading among the Russian soldiers and the civilian population. In order to get the situation under control, the leadership in Moscow sent Zinaida Vissarionovna Yermolyeva, one of the USSR’s leading microbiologists, to Stalingrad. Because the city was cut off from medical supply lines, Yermolyeva devised a plan to make use of the natural predators of the cholera bacterium. She set up a production facility for bacteriophages and thus created enough anti-cholera suspension to treat 50,000 people a day. After just a few days, the epidemic in the city had been stopped. In the decades since then, the fact that phages can be extremely effective in the struggle against bacteria has been forgotten in many places. However, in recent years researchers have once again been focusing more intensely on phage-based therapy. Bacteriophages—or phages for short—are viruses that select highly specific bacteria as hosts for their own multiplication process. For example, a phage that attacks cholera bacteria can infect only these bacteria, not human or animal cells. As a result, phages can be handled safely. Like all viruses, they dock onto their target bacterium, inject their genetic information, and reprogram it to produce additional phages after the infection—until no host bacteria are left.