The use of poison gas in World War I was a major military innovation. The gases used ranged from disabling chemicals such as tear gas and the more severe, mustard gas to killing agents like phosgene. This chemical warfare was a major component of the first global war and first total war of the 20th century. The killing capacity of gas was limited — only 3% of combat deaths were due to gas — however, the proportion of non-fatal casualties was high and gas remained one of the soldiers' greatest fears. In that it was possible to develop effective countermeasures to gas, it was unlike most other weapons of the period. Hence in the later stages of the war as the use of gas increased, in many cases its effectiveness was diminished. This widespread use of these agents of chemical warfare, and wartime advances in the composition of high explosives, gave rise to an occasionally expressed view of World War I as "the chemists' war".