Complex sentence: Through the U.S Navy ROTC program, he received his commission in the United States Navy as an Ensign, and served in the Navy from 1959 to 1961, attaining the rank of Lieutenant (Junior Grade).
Split into simpler sentences: Through the U.S Navy ROTC program, he received his commission in the United States Navy as an Ensign. Durkin served in the Navy from 1959 to 1961, attaining the rank of Lieutenant (Junior Grade).