Dulce et Decorum Est: Great War Trail of Cthulhu (2014)

Publisher Blurb:
This collection of adventures considers the Great War, 1914-18, from the perspective of Trail of Cthulhu. From the conflict in the air, to the depths of the sea, the home front and the different battle fronts, the Great War affects the lives of countless millions of people. It also brings humanity into conflict with elements of the Mythos, and in particular the Charnel God Mordiggian who, for the first time in centuries, may actually have more to devour than it can stomach.

The forces of the Gods do not take kindly to being disturbed, and nor do they usually play favourites; unless your players are careful, they may find themselves attacked and wiped out in an instant, caught in an otherworldly crossfire they can only hope to survive, not understand.