[ansel12]

In 1941, Army reserves Lieutenant Reagan was still in the horse cavalry, his fifth year of it.

[Ken H]

Summary of Reagan's military service. Last line is the best =>

Reagan’s Reserve Commission automatically terminated on 1 April 1953. However, he became Commander-in-Chief of all U.S. Armed Forces when he became President on 20 January 1981.

http://www.reagan.utexas.edu/archives/reference/military.html