The program was headed by major Félix Verdeja Bardales and led to the development of four prototype vehicles, including a self-propelled howitzer armed with a 75 millimeters (3.0 inches) gun.

[10] Due to the failure of Spanish efforts to produce a tank, and the ineffective attempts to procure foreign designs such as the Italian Fiat 3000,[11] by the start of the Spanish Civil War there were only ten working FT light tanks available in the country, plus the four Trubia A4s, involved at the time in the siege of Oviedo.

[16] In order to re-equip Nationalist armored forces with the T-26, German Major Ritter von Thoma offered Spanish troops 500 pesetas for each tank captured.

[17] There were also attempts to up-gun the Panzer I with an Italian Breda 20 millimetre Model 1935 anti-aircraft gun, due to its high Muzzle velocity and low recoil.

[21] The prototype was manufactured from spare parts and equipment scavenged from other light tanks, and featured a rectangular turret with 16 millimetres (0.63 inches) basic armor.

The chassis was divided into four quarters, with the forward right half occupied by the engine, gear box, clutch and final drive, beside the driver.

The rear half of the vehicle was taken up mostly by the turret basket and forty-six 45 millimetre rounds, as well as two 60 liter (13 Imp gal) fuel tanks.

The vehicle was powered by a Ford Model 48 engine taken from a civilian automobile, displacing 3,622 cc (221 in3) and producing 85 hp (63 kW) at 2,000 rpm.

The Verdeja prototype used the Panzer I's Aphon PG-31 gearbox, although this worked at excessive revolutions for the engine, offering less torque which made slopes greater than 40° difficult.

The vehicle's hull was elongated and the rear plate sloped, while the fuel capacity—and thus combat range—was increased, as was the ammunition capacity and the thickness of the armor.

[26] A major external difference between the previous model and this prototype was the new, low-profile turret which allowed the 45 millimetre gun to depress and elevate from 8° to 70°.

[29] During the testing the Verdeja traveled for some 500 kilometres (310 miles) without any maintenance problems, the only issue being the large consumption of water by the gasoline engine, due to the lack of an efficient radiator, and the loss of a rubber liner of one of the roadwheels.

[30] Testing completed, the prototype was returned and several problems were fixed, including engine deficiencies, the elevation of the sprocket and an increase to 10 millimetre of armor on all areas that had less.

Simultaneously, in case of failure of talks between Ford and Spain, the government also began to contact a number of German companies, including Maybach.

Another attempt was undertaken at contracting the ADESA (Armamento de Aviación, S.A.) company, to manufacture two Verdeja light tanks for experimental purposes.

Despite the failure to procure an engine, ADESA offered to construct 300 units, but these attempts failed and the program was abandoned by 1941.

H's and ten Sturmgeschütz IIIs into the Spanish Army in late 1943,[35] as well as failed attempts to procure one hundred more Panzer IVs and even Panthers and Tigers during 1944.

The fate of the self-propelled piece was much the same as that of the Verdeja 2, and the vehicle was left untouched at the proving grounds in Carabanchel until 1973, when it was moved to the Spanish base Alfonso XIII, housing the then Mechanized Infantry Regiment Wad Rass nº 55.

[44] Major changes to the original Verdeja 1 included removing the turret and replacing it with a gun shield with 10 millimetre thick steel armor.

The howitzer was designed as a monoblock steel tube, using a double-baffle muzzle brake, with twelve twists completing a full turn every forty calibers.

The crew could stow eight rounds of ammunition in a ready-round stowage area near the walls of the gun shield on each side of the breech, allowing easy access to projectiles.

A unique feature of this prototype was a mechanical brake built into the idler-wheel to the rear of the chassis, guaranteeing the vehicle's stability when firing and avoiding damage to the transmission.