Totskoye nuclear exercise
The Totskoye nuclear exercise was a military exercise undertaken by the Soviet Army to explore defensive and offensive warfare during nuclear war. The exercise, under the code name "Snowball" (Russian: Снежок, romanized: Snezhok), involved an aerial detonation of a 40 kt RDS-4 nuclear bomb.
Source: Wikipedia — Totskoye nuclear exercise (CC BY-SA 4.0)