Six Weeks is a book Tom Ricks recommended at the Best Defense blog. The title refers to the average lifespan of a junior officer in the British Army assigned to the Western Front. It's good, although given to the rosy. The writer organizes his work by the phases in an officers life, education, training, etc. and uses lots of quotes from memoirs, letters, biographies.
He notes early on there was 5 inch difference in height between the (upper class) officers and the "other ranks"-enlisted men. That's rather shocking, a dismal reflection on the British class system. But then there's this difference in our own class system: having a college education makes a difference in lifespan of over 10 years.