Call of Cthulhu: Red, White and Blacker than Black
No public information is currently known on Delta Green.
Kristina Maximoff stated Delta Green is a secret government funded organization intended to deal with the paranormal. Delta Green was formed in 1942 out of the remnants of something called P-Division. The organization had agents involved in the European Theater of World War II and was involved with something called Project Lunacy, seemingly focused on fighting The Karotechia during the fall of Berlin.
Delta Green uses a cell structure, which each cell receiving oversight from the executives but left to act independently in investigations. Each cell is run by one head investigator who reports to Cell A. Most agents in Delta Green are government employees or at least hold a title indicating such, which gives the organization unparalleled access to files and information that being a part of no single organization could grant them.