Douglas enlisted in the United States Navy in February 1969 and completed boot training at San Diego, California, in May 1969. He attended DT "A" school at Great Lakes Naval Training Station through September 1969 and was assigned to Staff at Great Lakes Naval Base through September 1971. He attended Field Medical School at Camp Pendelton, California, until December 1971 when he was assigned to the Marine Aircraft Wing at MCAS Iwakuni, Japan, where he served through December 1972. Douglas was released from active duty with the rank of DTI. His reserve duty continued until his honorable discharge upon end of enlistment in February 1975.