Initial Ausf. D were equipped with the Nebelwurfgerät with the later Ausf. A and Ausf. G receiving the Nahverteidigungswaffe. The front of the turret was a curved thick cast armour mantlet. Its transverse-cylindrical shape meant that it was more likely to deflect shells, but the lower section created a shot trap. If a non-penetrating hit bounced downwards off its lower section, it could penetrate the thin forward hull roof armour, and plunge down into the front hull compartment. Penetrations of this nature could have catastrophic results, since the compartment housed the driver and radio operator sitting along both sides of the massive gearbox and steering unit. Also, four magazines containing main gun ammunition were located between the driver/radio operator seats and the turret, directly underneath the gun mantlet when the turret was facing forward. From September 1944, a slightly redesigned mantlet with a flattened and much thicker lower "chin" design started to be fitted to Panther Ausf G models, the chin being intended to prevent such deflections. Conversion to the "chin" design was gradual, and Panthers continued to be produced to the end of the war with the rounded gun mantlet. The Ausf A model introduced a new cast armour commander's cupola, replacing the forged cupola. It featured a steel hoop to which a third MG 34 or either the coaxial or the bow machine gun could be mounted for use in the anti-aircraft role. The first Panthers (Ausf D) had a hydraulic motor that could traverse the turret at a maximum rate of one complete revolution per minute, independent of engine speed. This was improved in the Ausf A model with a hydraulic traverse powered by the engine; one full turn took 46 seconds at an engine speed of 1,000 rpm but only 15 seconds if the engine was running at 3,000 rpm. This arrangement was a weakness, as traversing the Panther's turret rapidly onto a target required close coordination between the gunner and driver, who had to run the engine to maximum speed. By comparison, the M4 Sherman's electrically or electro-hydraulically traversed turret rotated at up to 360 degrees in 15 seconds and was independent of engine speed, which gave it an advantage over the Panther in close-quarters combat. A hand traverse wheel was provided for the Panther gunner to make fine adjustment of his aim. Ammunition storage for the main gun was a weak point. All the ammunition for the main armament was stored in the hull, with a significant amount stored in the sponsons.