Japan, like other nations designing tanks, also developed self-propelled guns based on a standard tank chassis, that of the Chi-Ha. There were four main models, all of which employing a gun mounted on an open-topped Chi-Ha chassis, behind a fairly large shield which provided nominal protection from the side. The main difference between the types was the gun each carried. The "Ho-Ni 1" mounted the 75mm Type 90, the "Ho-Ni 2" fitted instead with the 105mm Type 91 field howitzer, (sometimes the Japanese 105mm howitzer was designated as the Type 91 and references to it as the "Type '31" refer to the year it was introduced in the western calender, but not the one the Japanese were using for designating weapons design), and the "Ho-Ni 3" was provided with the powerful 75mm Type 88 anti-aircraft gun. The "Ho-Ro," which might have been the first to appear, carried the 150mm howitzer, one of the most effective weapons of the Japanese field artillery. None of these vehicles ever saw service in numbers large enough to make a difference, and in fact there were so few built that they were only rarely encountered by advancing Allied forces. Sold Out!