I purchased one of these from Ebay:

http://www.guysoflidar.com/museum/th...radar-detector...

They show up occasionally on Ebay; first manufactured in 1961, when
the police in some states were use X-band radar to detect speeding
vehicles. They may not be sufficiently sensitive to pickup a ships
radar in time to be of any use, but at $20 they are worth testing
versus the $500 C.A.R.D.

Cheers, Jim