Complex sentence: Upon the outbreak of World War II, Gilormini offered his services to the Royal Air Force and served with them until November 30,1942, when he joined the United States Army Air Force with the rank of second lieutenant.
Split into simpler sentences: Upon the outbreak of World War II, Gilormini offered his services to the Royal Air Force and served with them. He served with the RAF until November 30,1942, when he joined the United States Army Air Force with the rank of second lieutenant.