Vehicle troops are decreasing and disappearing after I attacked enemies. Why?

Every time you fight or get attacked, it comes with a cost. Your troops will be injured or killed often, whether by other Bases or zombies, Wendells etc. You counter this fact with a very strong Hospital Power and Train, Train, Train more Troops. For future reference, pay no attention to the Clone Lab. It is a total waste of your rss. Better to leave those dead and train new ones. You’ll thank me later.