In theory, the idea of an armored box with a lot of weapons seemed sound. In practice, however, the large design was far from perfect. The vehicle was top-heavy, making it impractical to be used on uneven terrain. It was slow as well, often meaning that it could be outpaced by the very infantry it was to assist. The short tracks of the tractor system also made the vehicle relatively unsafe and uncontrollable in some cases. If the A7V has one saving grace, it was that the all-around armor protection for the crew was second to none - even when compared to the British designs - over an inch in some areas. Twenty of these tanks were produced, and the first of these were ready in October 1917. The A7V was first used at St Quentin on 21 March 1918. Although some of its features, such as the sprung tracks and the thicker armour, made it better than British tanks at that time, the A7V was less successful as a battle vehicle. The main problems concerned its mechanical reliability and the difficulty it encountered crossing enemy trenches. Three of the five tanks committed broke down at St Quentin. At the Second Battle of Villers-Bretonneux a British tank disabled one A7V and drove off two more.