In the 1950s, the United States planned to drop a nuclear bomb on the moon

At the time, the US was lagging behind the Soviet Union in the space race (For example, they sent a man into space before the US did.) Exploding a nuclear weapon on the moon was a way to one-up the Soviet Union. They planned on nuking the moon as a PR stunt, and they wanted to make sure the explosion could be seen from Earth!

This was part of a top-secret Air Force project, "Project A119" which was called "A Study of Lunar Research Flights". Details of the 1958 plan were made public in 2000 by Dr. Leonard Reiffel, the physicist who ran the project. He had worked on the project with famous astronomer Carl Sagan.
Sagan may have also disclosed some of this top-secret information when he applied for the prestigious Miller Institute graduate fellowship to Berkeley. At the time, Sagan thought that a nuclear explosion could reveal whether there was life on the moon.
The explosion likely would have ruined the face of the "man on the moon". Thankfully, years later they decided to send Neil Armstrong to the moon, and not a nuclear bomb.