The USA tried to keep secret from the USSR.

The Manhattan project

Explanation:

The Manhattan project was a secret project that's developed by United States in 1942. The main goal of this project was to create the first weapon of mass destruction that utilize nuclear energy.

Initially, USA tried to keep this a secret from the Soviet Union.

But the project was leaked to the Soviet Union by Julius and Ethel Rosenberg who were recruited as Soviet's spy. Ethel's brother David Greenglass worked in Manhattan project and supplied Julius with the information.

a.

congress passed laws allowing for free passage between states.