German assistance in the military was not limited to personnel training and reorganisation but also included military hardware. According to von Seeckt, around 80% of China's output of weapons were below par or unsuitable for modern warfare. Therefore, projects were undertaken to modernise existing arsenals. For example, the Hanyang Arsenal was reconstructed in 1935 and 1936 to produce Maxim machine guns, various 82 mm trench mortars, and the Chiang Kai-shek rifle (based on the German Mauser Standardmodell and Karabiner 98k rifles). The Chiang Kai-shek and Hanyang 88 rifles remained as the predominant firearm used by Chinese armies throughout the war. Another factory was established to produce gas masks, but plans for a mustard gas plant were eventually scrapped. In May 1938, several arsenals were built in Hunan to produce 20mm, 37 mm, and 75 mm artilleries. In late 1936, a plant was built near Nanking to manufacture binoculars and sniper rifle sights. Additional arsenals were built or upgraded to manufacture other weapons and ordnance, such as the MG-34, pack guns of different calibres, and even replacement parts for vehicles of the Leichter Panzerspähwagen. Several research institutes were also established under German auspices, such as the Ordnance and Arsenal Office and the Chemical Research Institute, under the direction from IG Farben. Many of those institutes were headed by Chinese engineers who had returned from Germany. In 1935 and 1936, China ordered a total of 315,000 of the M35 Stahlhelm and many Gewehr 88, 98 rifles and the C96 Broomhandle Mauser. China also imported other military hardware, such as a small number of Henschel, Junkers, Heinkel and Messerschmitt aircraft, some of them to be assembled in China, and Rheinmetall and Krupp howitzers, anti-tank, and mountain guns, such as the PaK 37mm, as well as armoured fighting vehicles such as the Panzer I.