Some were told that it was to check their posture. Others, to check them for rickets. But actually it was the pet project of Columbia University Professor William H. Sheldon (1898-1977) and Harvard University Professor Earnest Hooten (1887-1954), who said they were interested in somatotyping.
Classifying human bodies by size and shape, and determining how those shapes influenced personality.
They had already taken nude photos of 400 undergraduate men at the University of Chicago and 200 juvenile delinquents in Boston. Hooten died in 1954, but Sheldon continued, photographing men in the military, in hospitals, in colleges, in prisons, until by the end of his life he had accumulated 200,000 photographs of men and 2,000 of women.
But you can see some samples online, and several hundred in Sheldon's book, Atlas of Men (1954), with clever little taglines comparing them to animals: "paleolithic tiger," "dugongs and manatees."
Sheldon divided male bodies into three types: endomorph (fat), mesomorph (muscular), and ectomorph (skinny), and discovered that juvenile delinquents were likely to be mesomorphs, while Ivy League freshmen were more likely to be ectomorphs.
Nice to know when you're cruising.
An obsession with taking nude photographs of young men. Were Sheldon and Hooten gay?
Neither married women, but Hooten spearheaded the famous purge of Harvard "homosexuals" in 1920, along with his friend and roommate Lester Wilcox.
Maybe he was protesting too much.