In the October 1918 issue of Electrical Experimenter magazine, science fiction pioneer Hugo Gernsback revealed his vision for a nigh indestructible war engine. Gernsback — who also devised such retrotech killing machines as the riot control droid and the anti-gangster sky bobsled — regaled readers with the automatic soldier, a Dalek-like machine who is unfazed by the horrors of trench warfare. Given that this was written in the waning days of World War I, Gernsback touted these robot warriors as a more humane options:
As science advances, and as all sorts of infernal machines are thrown into a modern war, the men in the front line trenches become less and less anxious to bear the full brunt of high explosive shells, gas attacks, liquid fire and what not. No matter how courageous a body of soldiers, their morale is bound to deteriorate considerably under a murderous mustard gas attack, or under a modern barrage [...]
The automatic soldier is not dependent upon the rear for victuals, as the only thing it eats are munitions with which it can be supplied at night by way of trenches. It is not affected by shell shock nor mustard gas, and liquid fire has no effect upon it. It never surrenders and never turns traitor.
For more robot armies that never came to pass, check out the BBC article Robot history: The rise of the drone by Paleofuture Blog's Matt Novak.