Complex sentence: He took up the appointment of Military Secretary to the India Office in April 1926 and, having been promoted field marshal on 30 November 1926, he remained at the India Office until he retired in May 1930.
Split into simpler sentences: He took up the appointment of Military Secretary to the India Office in April 1926. He was promoted field marshal on 30 November 1926 and remained at the India Office until he retired in May 1930.