That's a lie! Emperor Karl tried to prevent the use of poison gas but was unable to do so. Beatifying the saintly emperor was in my opinion the best act of Pope John Paul II's pontificate.
sorry it's not a lie, you've been fooled by the propaganda bandied about by his descendants. The facts speak for themselves, he was emperor, his troops used poison gas, and he didn't forbid it. But in his defense, just about every other army in that war used it too.