In the later ages of human warfare, pokemon remained participants, but were primarily reduced to support roles by the rise of faster-firing, more accurate guns. The great exception to this were the Chesnaught, who had no issues walking across trenches and enduring machine gun fire, because they are immune to bullets.
Chesnaught's defenses are strong even by pokemon standards; they are capable of withdrawing into a spiky shield which harms the opponent while shrugging off damage, although they can not maintain this defense long. This minimal wound is far more damage than human weapons can deal the Chesnaught, whose strong defenses against contact attacks were equally effective against bayonets.
Chesnaught were responsible for most of the few successful offensives in the age of trench warfare, and the most likely human soldiers to survive these attacks were those who were stationed directly behind these pokemon. Efforts to defeat them the old fashioned way, with other pokemon, were broken by machine gun fire, so any battle where both sides could claim Chesnaught soon devolved into the mother of all Chesnaught battles, with whole armies reduced to the role of spectators. Innovative weapons such as flamethrowers or Vileplume gas could at times break the stalemate, but lacked the accuracy to guarantee harming only the opposing Chesnaught, and few soldiers had any wish to defeat both sides of pokemon and resume throwing their lives away through futile machine-gun charges.
Today, long after Chesnaught have turned some of the deadliest conflicts of human history into an utter farce, they are a far rarer sight on Kalos' high-level pokemon battlefields. Yet humanity must count itself lucky that Chesnaught are a solitary pokemon in the wild, for all the technology of modern Man still struggled to bring them down.
