The aircraft carrier's entrance into the sea was its second since November 2016, when the vessel stopped its Japanese home port for technical maintenance. Previously, it had left the port for the sea on May 8.
The exact area and deadlines of the tests are yet unknown.
The Nimitz-class USS Ronald Reagan is equipped with two nuclear reactors and was deployed at the Yokosuka base as part of the US strike group. It is capable of transporting 80 aircraft and up to 5,500 personnel.