90 75 mm field gun mounted in an open casemate with frontal and side armour only. They entered service in 1942 and were first deployed in combat at the Battle of Luzon in the Philippines in 1945. Some were used in static entrenched positions. A variant, known as the Type 1 Ho-Ni II mounted a Type 91 105 mm howitzer and had a slightly changed superstructure as far as the side armor with re-positioned observation visors. Production began in 1943, with only 54 completed. The other variant produced was the Type 3 Ho-Ni III, which mounted a Type 3 75 mm tank gun in a completely enclosed armored casemate to address the issue of crew protection in close combat. The welded superstructure had sloped armour and the gun mount had additional stamped armour plate. The total number produced of all three types in the Ho-Ni series were 111 units. Most of the Ho-Ni units were retained within the Japanese home islands to form part of the defenses against the projected American invasion, and did not see combat before the surrender of Japan. The Type 2 Ho-I Gun tank used the Type 1 Chi-He medium tank chassis. It was designed as a self-propelled howitzer, mounting a short barreled Type 99 75 mm gun to provide close-in fire support. For deployment, the gun tank was intended to be used in a fire support company for each of the tank regiments. No Type 2 Ho-I gun tanks are known to have engaged in combat prior to Japan's surrender. The prototype was built in 1942 and 31 units were produced in 1944. The Type 4 Ho-Ro self-propelled artillery used a modified Type 97 chassis. On to this platform, a Type 38 150 mm howitzer was mounted. The main gun could fire Type 88 APHE rounds and HEAT rounds. Given its breech loader, the maximum rate of fire was only 5 rounds per minute. The gun's elevation was restricted to 30 degrees by the construction of the chassis. Other design issues included the fact that although the gun crew was protected by a gun shield with armour thickness of 25 mm at the front, the shield only extended a very short distance on the sides; leaving the rest of the sides and back exposed. They were rushed into service, deployed and saw combat during the Philippines Campaign in the last year of World War II.