Defcon 3 is an unofficial multiplayer maps "expansion pack" for C&C1 and Red Alert 1. It contains over 300 maps in total for both games. It is a CD compiled by a company called Head Games. It consists of fan maps collected over the Internet and it appears this "expansion pack" was released in 1996.

Full map previews for every map can be found at http://www.flickr.com/photos/107027902@N04/sets/72157637090598873/