 Between late 1937 and 1938, Captain Félix Verdeja Bardales began to privately develop the concept for a new light tank. The new tank would take into consideration all the qualities and problems with existing tanks in service with the Nationalist Army, including the Panzer I and T-26, and combine a number of characteristics which would make it the best light tank in service at the time. His ideal light tank included a 45-millimeter (1.8 in) tank gun, with 360-degree traverse and an elevation of 72 degrees. At the same time, the vehicle was to have the lowest possible silhouette, and no less than 15 millimeters (0.59 in) of all-around armor, and 30 millimeters (1.2 in) on the front. Furthermore, the armor was to be sloped to maximize its efficiency and chance of an incoming projectile ricocheting. With a maximum velocity of 70 kilometers per hour (43 mph), the light tank was to be powered by a 120 horsepower (89 kW) engine. Furthermore, the vehicle's mechanical reliability was to improve upon that of the existing tanks in service with the Nationalist Army. Despite initial obstacles, including opposition to an indigenous Spanish tank program from German General Wilhelm Ritter von Thoma, the first prototype was delivered in late 1938; this prototype was built from spare parts taken from a number of different tanks. The prototype performed well in testing and a new prototype was ordered.
