This piece originally ran in the May 2023 issue of EAA Sport Aviation magazine.

Introduced in 1939, the View-Master system used stereoscopic photography printed on cardboard disks to display 3D images in a purpose-built viewer. During World War II, more than 100,000 viewers and millions of slides were produced for the U.S. military to train recruits in airplane and ship identification and range estimation. The View-Master system endured after the war, becoming a popular children’s toy.