Complex sentence: It did not take him long to escape and rejoin his squadron, as he was promoted from Maréchal-des-logis to Adjutant on 20 July 1917 and wounded by shrapnel on 13 August 1917.
Split into simpler sentences: It did not take him long to escape and rejoin his squadron. He was promoted from Maréchal-des-logis to Adjutant on 20 July 1917 and wounded by shrapnel on 13 August 1917.