Disclaimer I have never worked with crypto machines and do not have access to any classified information. No classified information appears on this or any of my other web pages. All the information is from open sources such as the internet and non classified manuals. Army crypto gear, CSP-488 is the Navy name.
The M-138-A is a strip cipher version. Used through the end of W. Used with a large number of radios for both voice, fax and data. Used with PRC-104 and other H.
What encryption system, what will it interoperate with? Replaces the KY-57 and other equipment. Uses a 40 character key based on 5-level paper tape. Originally designed to work with the PRC-77. Uses thumb-wheel switches to set key.
There may be a shut down function that works by unit serial number. PSN-11 GPS Receiver Can use a crypto key for reception of the GPS L2 frequency. Quantic Q5200 GPS Time Receiver Can use a crypto key for reception of the GPS L2 frequency. ASN-169 Version of the Trimpack that decodes encrypted L1 to avoid problems when SA was turned on. Requires key load for encrypted signals but works as civilian receiver without keys. This is the most common digital data application. Q modulation for Tx and Rx.
Most likely that the missing control box contains some type of encryption that would allow the spy to compose a message in the field and send it as well as decrypt an incoming message. This would require inputting a key. If the missing control box did not contain any crypto function it may not have been destroyed. That’s an area that I’m interested in, but not one where I have a collection of equipment.