Tanks were adapted to a wide range of military tasks, including engineering. Specialized models, such as flame-thrower tanks, armored recovery vehicles for towing disabled tanks from the battlefield, and command tanks with extra radios were also used. Some of these tank variants live on as other classes of armored fighting vehicle, no longer called "tanks". All major combatant powers also developed tank destroyers and assault guns, as armored vehicles carrying large-caliber guns, but often no turrets. Turreted vehicles are expensive to manufacture compared to non-turreted vehicles.