One of the earliest documented instances of the concept of sloped armour is in the drawing of Leonardo da Vinci's fighting vehicle. Sloped armour was actually used on nineteenth century early Confederate ironclads, such as CSS Virginia, and partially implemented on the first French tank, the Schneider CA1 in the First World War, but the first tanks to be completely fitted with sloped armour were the French SOMUA S35 and other contemporary French tanks like the Renault R35, which had fully cast hulls and turrets. It was also used to a greater effect on the famous Soviet T-34 battle tank by the Soviet tank design team of the Kharkov Locomotive Factory, led by Mikhail Koshkin. It was a technological response to the more effective anti-tank guns being put into service at this time.