From Diego Garcia to San Diego, Navy Medicine West boasts 10 hospitals, two dental centers, 51 branch clinics and about 675,000 patients, making it one of the largest health-care networks on Earth. And now it has a new skipper — Rear Adm. Paul D. Pearigen, chief of the Navy Medical Corps. He replaced Rear Adm. Bruce L. Gillingham during a Monday morning ceremony at the headquarters’ campus north of San Diego Naval Base.