The Chinese army appears to have fielded a brand-new light tank suitable for mountain warfare. New photos depict the diminutive fighting vehicle, which China has reportedly dubbed “ZTQ,” trundling across rough terrain. The ZTQ, which Beijing apparently developed in order to help defend China’s western land border, is impressive in a lot of ways—and not the least because the U.S. Army, the world’s leading ground combat force, tried and failed for years to acquire a similar vehicle. More and more, Beijing is matching American military capabilities with new warships, stealth fighters and combat helicopters. The ZTQ represents one military niche...