Not surprisingly, older tanks have a higher rate of system failure than new ones. This was recently seen from an examination of years of vehicle records for units operating at the U.S. Army National Training Center. Older M-1 tanks, with an average age of 14 years, had a 74 percent operational readiness status, while tanks that were less than three years old had an a 84 percent operational readiness. The older tanks tended to have about twice as many problems as the new ones. No big surprise there. However, many of the problems were not the kind that would prevent sending the tank off to battle in wartime. The official operational readiness standards dont tolerate minor leaks, but troops in combat can put up with that sort of thing. Similar equipment irregularities in other parts of the tank are equally tolerable when its a matter of life and death. The more stringent peacetime standards mean that there will be more tanks available for action in wartime. It actually works that way, at least for American forces. From 1991 to 2003, American units in combat zones were consistently able to keep over 90 percent of their armored vehicles moving and fighting. 

Not surprising, but useful to know. The Russians made the most of this "new tank reliability syndrome" throughout the cold war. They kept most of each regiments tanks little used, and did most of the training on a few "training tanks" that were often out of action because they needed repairs. Many nations don't use their armored vehicles much, because of the effort and expense needed to keep them maintained.