The T-55 tank series is the most widely used tank in the world and has seen service in over 50 countries. Modifications to the T-54/55 series over the years have changed almost every aspect of the vehicles. Initially, Soviet modifications included a better turret shape, improved NBC protection, and an improved powerplant. Later, improved fire-control equipment and night-vision equipment was added. Foreign improvements, both in Warsaw Pact nations and elsewhere, have further improved protection, power, and firepower. T-54/55s have been re-armed with improved tank guns, AA machine guns, advanced armor arrays, and technologies, such as laser range finders and computerized fire control systems, that did not exist when the tank was first being built.