This anonymous poster from World War I carries a potent image of St. George slaying the dragon, an appeal that is at the same time political and religious; St. George is the traditional patron saint of both Great Britain and the Anglican Church.
The dragon, representing Germany of course, still has the power to remind us of its old associations with Satan and the anti-Christ; this is how Spenser used the image in The Faerie Queene, for example. Shakespeare uses St. George for political ends in Henry V and the rousing exhortation to his troops as they assault the city of Harfleur: "Follow your spirit; and upon this charge / Cry 'God for Harry! England and St. George!'"
Knights and dragons seem to have been serviceable images for both the Allies and the Central Powers, and the Germans had their own versions of the St. George posters.