In February 1941, Bernstein was drafted into the U.S. Army. Eventually attaining the rank of Sergeant, he spent most of World War II as a correspondent on the staff of the Army newspaper Yank, filing dispatches from Iran, Palestine, Egypt, North Africa, Sicily and Yugoslavia. He wrote of his experiences in Palestine in an article entitled "War and Palestine".

Bernstein wrote a number of articles and stories based on his experiences in the Army, many of which originally appeared in The New Yorker. These were collected in Keep Your Head Down, his first book, published in 1945.