Complex sentence: After just two years, on 9 April 1917, he was promoted to second lieutenant but shortly after, at the age of thirty-eight, he was killed in the British offensive at Arras by the blast of a shell.
Split into simpler sentences: After just two years, on 9 April 1917, he was promoted to second lieutenant. Shortly after, at the age of thirty-eight, he was killed in the British offensive at Arras by the blast of a shell.