This is an image of some of the gas masks worn by soldiers in World War One. These were made for soldiers to wear since the trenches the soldiers were fighting were very nasty and riddled with bacteria and diseases (obviously). On top of that, chemical warfare was a tactic being used mostly by the Germans and these masks were used to protect the allied soldiers from these attacks. In the poem "Dulce Et Decorum Est", Wilfred Owen briefly talks about these gas attacks in lines 9-12 saying "Gas! GAS! Quick, boys!—An ecstasy of fumbling Fitting the clumsy helmets just in time, but someone still was yelling out and stumbling And flound'ring like a man in fire or lime." The Germans were the first to utilize chemical weapons during WWI in 1915 in Ypres, Belgium (https://www.sciencehistory.org/distillations/a-brief-history-of-chemica…).