Complex sentence: According to his DD214 from the website for "Double Agent", Sam rose to the rank of Lieutenant Commander (O-4) in the Navy, during which he spent nearly three years (2 years, 11 months) as an intelligence analyst.
Split into simpler sentences: According to his DD214 from the website for "Double Agent", Sam rose to the rank of Lieutenant Commander (O-4) during his time in the Navy. While in the Navy, he spent nearly three years (2 years, 11 months) as an intelligence analyst.