This article addresses an episode in the history of the First World War and its immediate aftermath that has previously been overlooked: the establishment of professional guide dog training in interwar Germany. The brutal, mechanized nature of warfare produced some of the most gruesome injuries ever seen. A significant number of blind veterans suffered no physical injuries other than the loss of their eyesight; they were still young, relatively fit and eager to return to work. It was this group in particular which stood to benefit enormously from the implementation of guide dog training. Under this scheme, which the German state initially made available to war veterans in 1916, dogs became helpers, and, furthermore, equal partners to disabled soldiers. This article shows how the resultant cooperation between guide dogs and their owners placed the human–animal bond on a new footing. It evaluates the significance of guide dogs both within the narrow context of ‘prosthesis production’ and the wider context of the rehabilitation system adopted by the Weimar Republic. It also seeks to contribute to the history of animals by emphasizing the significance of the war as an interspecies moment. Within this context, this article demonstrates how the partnership of mutual trust forged between guide dogs and their human companions had its roots in wartime, when soldiers often came to regard animals almost as an extension of themselves. This article reveals that guide dogs performed a variety of roles. On a mundane level, they fulfilled an economic function, reducing the burden on paid attendants, spouses and friends, and enabling their masters to get to their workplaces independently. They were mobility aids – living prostheses – who effectively replaced the eyes of blinded soldiers, albeit figuratively. They also provided companionship and emotional support in a way that was reminiscent of the comfort nurses gave injured soldiers during the war. Significantly, the social, economic and emotional impact of guide dogs went far beyond the partnership they forged with their owners; it affected those in their immediate environment and society as a whole. The common experience of guide dog ownership led to the development of a distinct identity and ‘emotional community’ among blind ex-soldiers, as well as boosting their self-confidence, which in turn inspired them to assert their rights and negotiate their citizenship in new ways. Even more remarkable is the broader significance of the German experiment, which acted as a catalyst for the successful employment of guide dogs on a global scale, enabling thousands of blind people – the majority of whom were civilians – to benefit from the scheme.