Reginald J. Johnson was born in New York in July 1896 to Samuel J. Johnson, a tinsmith, and Kate M. Johnson. The family lived in Webster, N.Y. Reginald enlisted in the United States Navy in June 1917. In October 1917, after training at the United States Naval Training Station in Newport, Rhode Island, he joined the crew of the USS Florida . He remained with the Florida for the remainder of his naval career, serving as a gunner and sheet metal worker. During the final year of World War I, the Florida was primarily stationed in Scotland, and saw little combat. The ship returned to the United States in December 1918 and spent time in New York, Norfolk, and Boston before sailing to the Caribbean.
Johnson remained with the Florida in Boston, Massachusetts, in the latter part of 1919. By early 1920, the ship again sailed to the Caribbean, and in July 1920 it returned to New York, where Johnson was discharged on July 26. He returned to Webster, New York.