The Type 89 Chi-Ro tank was lighter (9.8 tonnes) and shorter than the Chi-I. It contained increased armour (6 to 17 mm) and an improved water-cooled engine. After success in initial tests, the Type 89 became the first mass-produced Japanese tank. The Type 89 had a crew of four, and was armed with a 57 mm Type 90 gun and two 6.5 mm type 91 machine guns. The second version of this tank known as the Type89B Otsu used a diesel engine. The Japanese were among the first to use diesel engines in their tank designs.