The CSP-845 was the U.S. Navy's version of a strip cipher system, which played an important role in classified communications before and during World War II. At the beginning of the war, a great deal of reliance was placed on strip systems due to the shortage of cipher machines. It is a hinged aluminum board (14" × 12") into which there are 30 milled grooved channels designed to hold changeable paper strips containing random mixed alphabets. The method of operation changed several times during the war to improve the security of the system.