China's Guangzhou destroyer launching a missile during a military exercise in July 2016.Xinhua News Agency/Xinhua News Agency via Getty ImagesThe US Navy has long held a missile-tube advantage over China.But China's ships now have half as many vertical-launch-system cells as the US, research found.VLS capacity is important for naval combat, but it's not everything.China is closing the missile-tube gap with the US Navy as the latter's long-standing edge in vertical-launching-system cell capacity, one indicator of naval strength, shrinks.The People's Liberation Army Navy now has over half as many missile tubes, or VLS cells, as US Navy surface combatants have.