This file is a work of a sailor or employee of the U.S. Navy, taken or made as part of that person's official duties. As a work of the U.S. federal government, it is in the public domain in the United States.
United States en:SIGABA (ECM Mk II) cipher machine. Source: US Navy operating instructions, May 1944. Provided online by Richard Pekelney/Historic Naval Ships Association: http://www.hnsa.org/doc/crypto/ecm/index.htm {{PD-USGov-Military-Navy}}