696846 U.S. troops learn cryptography, Tarawa, Papua New Guinea, June 1943 (sepia photo) by American Photographer, (20th century); Private Collection; (add.info.: Operations in Papua New Guinea were essential to the U.S. Navy\'s drive across the Central Pacific and to the U.S. Army\'s liberation of the Philippine Islands from Japanese occupation. U.S. troops seen here learning cryptography on the M-209, a portable mechanical cipher machine used by the US military primarily in World War II.); Prismatic Pictures ; American, out of copyright.