Meanwhile, a set of wedge-shaped counterweights weighing 3,700 pounds total was designed by Fisher. The wedge-shaped weights began to be added to new vehicles at Fisher on 25 January 1943. By late December 1942, a second lock was added to the turret and a stirrup-shaped gun cradle was added to the rear deck to secure the gun for travel. Since the track grousers could not be stored on the rear of the turret anymore, grouser racks that could be attached to the appliqué armor bosses on the hull were added to vehicles beginning in early April 1943. The M10 initially lacked any provision for indirect fire. In May 1943, an azimuth indicator and gunner's quadrant were added to the M10. The grouser racks and indirect fire equipment were often retrofitted to earlier vehicles. By late June 1943, it was realized that Fisher's initial counterweights were too heavy. Two newly designed counterweights reduced the total weight to 2,500 pounds and better distributed the weight of the gun. They resembled an upside-down "duck bill" shape when viewed from the side. To accommodate the new weights, the design of the upper rear of the turret was changed from sloped inwards to nearly vertical. In July 1943, the appliqué armor bosses on the hull sides and turret were dropped from production. The bosses on the glacis were retained. In late September 1943, a single M10 was tested with an Oilgear hydraulic traversing motor that could traverse the turret even without the counterweights, but this modification was not pursued as the production contracts were reaching their end. Production of 4,993 M10s by the Fisher Body division of General Motors at the Fisher Tank Arsenal in Grand Blanc, Michigan ran from September 1942 through December 1943. Ford Motor Company built 1,038 M10A1s from October 1942 until September 1943. From September to November 1943, Fisher built the remaining 375 M10A1s. Fisher also completed a further 300 M10A1 hulls without turrets in January 1944 for direct conversion to M36 tank destroyers. From January to June 1944, 209 M10A1 vehicles were subsequently converted to M35 Prime Movers by removing the turret and adding the necessary equipment for them to tow the 8-inch Gun M1 and 240 mm Howitzer M1 1,413 M10A1s, including the 300 hulls manufactured in January 1944, and 724 M10s were eventually converted into M36 tank destroyers. Armament Primary The M10 tank destroyer used an M4A2 medium