Delta Green (1996)

Delta Green is a Call of Cthulhu sourcebook for modern day conflicts, licensed from Chaosium, Inc.

From the back cover:

Welcome to America at the end of the millennium. Do you Know who is pulling the strings?

Delta Green knows. Things from beyond space and time that lurk and titter in the shadows, the slow rot at the core of humanity, the dark stars that whirl madly above--these are the true masters of the world. Delta Green has been fighting them since the 1928 Raid on Innsmouth, and the fight still rages on.

This book is your weapon and your guide--the largest Call of Cthulhu sourcebook ever.

Inside you'll find a secret history of the 20th century, and the movers and shakers who are the players in the game: Delta Green, the outlaw conspiracy working inside the U.S. government to fight the darkness; Majestic-12, the clandestine agency that cuts deals with aliens and reports to no one; SaucerWatch, a UFO study group closer to the truth than they know; the Karotechia, immortal Nazis who serve a risen Hitler; and the Fate, an occult criminal syndicate that knows where the bodies are buried.

Plus: New skills; new spells; new weapons; new Mythos tomes; profiles of thirty-six real-world intelligence and law-enforcement agencies, with character templates for each; a look at Mi-Go biology, philosophy, and operations; analysis of the Cthulhu Mythos in the modern day; a factual history of the U.S. intelligence and law-enforcement community; dozens of useful NPCs; campaign construction guidelines; two scenarios; a short campaign; and more.

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"Delta Green fan"

The 2006 printing includes both BRP and d20 stats. It is not just d20. The new printing also includes numerous textual corrections and a map not included in the first version.