
One of the deadliest weapons to make its appearance in World War I was not a firearm of any sort, but rather a chemical. Mustard gas was first unleashed by the Germans in 1917, and it would cause horrific respiratory distress that would temporarily disable swathes of enemy soldiers affected by the gas. It also inflicted physical injuries in the form of blisters on the skin and even in the lungs.
Gas shells would be loaded with mustard gas and then fired into enemy lines, inflicting hundreds of thousands of casualties on both sides.