As good as the U.S. M-1 Abrams tank is, it does have some shortcomings. For one thing, it is very vulnerable to electronic warfare, because of its heavy use of electronics. While the tank is virtually invulnerable, all that laminated, depleted uranium, armor brings its weight up to 70 tons. This makes a lot of bridges impossible to use, and, in general, causes problems (like not being able to run safely in some city streets that have a lot of vaults and conduits underneath.) The weight also required a special, lightweight engine to provide lots of power without a lot more weight. This meant a 1500 horsepower gas turbine (jet engine, basically) that is a prodigious fuel hog. We're talking up to twelve gallons per mile. If involved in intensive operations, it needs to be refueled as frequently as every twelve hours. The previous generation of tanks never needed refueling more frequently than every 24 hours. Refueling in a timely fashion also requires fuel transfer pumps that, if they break, leaves you out of luck (and fuel). While the larger 120mm gun can knock out any other tank in the world, it means the M-1 carries only 40 rounds of ammo, compared to 63 rounds when the early M-1s had a 105mm gun. That big old gas turbine, and the general design of the tank makes it more difficult work with infantry. For one thing, the grunts can't easily climb on the outside of the M-1. The heat thrown out the back of the tank eliminates the phone that used to be on the rear of American tanks, so, especially in street fighting, the infantry could easily communicate with the tank crew. Despite all that, the M-1 has done very well in combat by skillfully using its assets and avoiding trouble with its liabilities. Some American tank designers still wish the U.S. had gone with one of the alternate designs, similar to the German Leopard, that were lighter and used a diesel engine. But the U.S. has over 5,000 M-1s available and it's unlikely that a new design will show up any time soon.