On August 4, German troops invaded Belgium, Britain had declared war on Germany and the fighting had started in earnest. There was a widespread feeling that the war would be short and decisive, despite the size of the armies involved. New weapons, it was thought, might provide a quick way to overcome any perceived advantage an enemy might have. Casualties in this modern war would not be excessive. By the end of the year, however, it was clear that not only would massive numbers of men need to fight but casualties would be immense. At least 300,000 Allied and 200,000 Central Powers soldiers were killed in five months, and there was a dawning realization that victory would come only after vast numbers of men and equipment had been thrown into the fray.

The images from this slide show depict a mix of old and new technologies and tactics vying for a place on the battlefields of 1914 as well as a look at some of the signal events of the early months of the war.

For a more comprehensive look at all the aspects of World War I—military, economic, social, technological—view our archive package, Scientific American Chronicles: World War I, at www.ScientificAmerican.com/wwi.