United States v Reynolds was a court case from 1954. The case started when three Air Force officers were killed in a plane crash. The families of the officers wanted to know what caused the crash and filed a lawsuit against the Air Force.
The Air Force refused to give the families information about the crash, claiming it was a secret. The families argued that they had a right to know what caused the crash and took it to court.
The court case, United States v Reynolds, was the first time the United States Supreme Court said that the government could keep some things a secret if they thought it was important to national security. The court ruled that the government could keep the documents a secret but still had to show that they were important to national security.