 In 1967, the German Ministry of Defense decided to re-open a Leopard 1 improvement program, known as the Vergoldeter Leopard ("Gilded Leopard"), later renamed the Keiler ("Wild Boar"). Krauss-Maffei was chosen as the contractor, and two prototypes were developed in 1969 and 1970. This program grew into the Leopard 2; the first prototype of the new tank was delivered in 1972, equipped with a 105-millimeter (4.1 in) smoothbore main gun. Between 1972 and 1975, a total of 17 prototypes were developed. The new 120 mm gun's ten-year development effort, which had begun in 1964, ended in 1974. Ten of the 17 turrets built were equipped with the 105 mm smoothbore gun, and the other seven were equipped with the larger 120 mm gun. Another program aimed to mount the 152-millimeter (6.0 in) missile-gun was also developed in an attempt to save components from the MBT-70, but in 1971 the program was ended for economic reasons. Instead, the Germans opted for Rheinmetall's 120 mm L / 44 smoothbore tank gun.
