In 1967, the Japanese Defence Agency commissioned for a new Armored Personnel Carrier as a planned successor to the Type SU-60, this original vehicle becoming the first APC to be produced in post-war Japan. Japan Ground Self-Defense Forces (JGSDF) required a modern vehicle with appropriate protection levels in a new age of armored combat as well as higher road speeds (37mph minimum) and improved internal space for up to nine infantrymen. Additionally, the hull would have to have amphibious capabilities to serve both marine and army units, gun ports for the occupants to engage from within the safety of the vehicle and protect against small arms fire and artillery spray. By any regard, this would become a very conventional APC of the Cold War years. The vehicle was taken on in 1973 and remains an active component of the JGSDF today (2014) with some 338 having been produced under the Mitsubishi Heavy Industries (MHI) brand label.
The new requirement fell to MHI and Komatsu, both major players in the heavy industry market. Each concern was charged with delivering a pair of prototypes - the first with a steel hull and the second with an aluminum hull - for evaluation to which the pilot vehicles arrived in short order during 1969. After years of trials, the Mitsubishi aluminum-hulled pilot vehicle was selected ahead of the Komatsu offering, bringing rise to the Type 73 APC line.
The end-product was a 14.5-ton vehicle with a running length of 19 feet, a width of 9.2 feet and a height of 7.2 feet. Its standard operating crew was four - driver, commander and primary gunner and bow machine gunner (optional) - with room for up to nine occupants. Primary armament was a single 12.7mm Browning M2HB heavy machine gun mounted at an emplacement along the turret roof. A 7.62mm Browning M1919A4 machine gun was fitted in a bow-mounted position. Power was served through a single Mitsubishi 4ZF air-cooled, 4-cylinder diesel-fueled engine developing 300 horsepower. Unlike other contemporary APCs, the Type 73 mounted its engine at the center of the hull. Running gear in the track-and-wheel arrangement included five double-tired road wheels to a hull side and a drive sprocket fore with the track idler aft. No track return rollers were used. The hull sat atop a torsion bar suspension system. The vehicle could then reach a maximum speed of 43 miles per hour on ideal surfaces. Operational range was out to 190 miles.
With the centralized engine placement, the internal seating arrangement of the Type 73 differed from competing designs of the period. The driver was seated at front-right with the bow machine gunner to his left. The vehicle commander then sat directly the bow gunner position. The primary gunner was seated at a station aft of the driver. As the engine then took up the space at center, the passenger cabin was at the rear. The primary gunner managed the heavy caliber machine gun with full 360-degree traversal of the weapon, able to cover all attack angled of incoming enemy aircraft, vehicles and infantry. The bow machine gunner, utilizing a machine gun held in a ball mounting, was offered only a limited firing arc, best suited for the infantry suppression role. Beyond its armament fitting, the Type 73 was also given six smoke grenade dischargers -fitted in two banks of three launchers each - and this used to help screen the vehicle during maneuvers.
The passenger compartment yielded firing ports along the sides of the hull. There were also additional firing ports at the twin entry/exit doors at the rear hull facing. The doors were hinged to open outwards, providing some ballistics protection for the exiting infantrymen. An NBC (Nuclear, Biological, Chemical) suite proved standard as did infrared equipment. While the designed to support amphibious operation, the Type 73 required preparation prior to entry of water sources. Additionally, it lacked any water jets, utilizing the moving action of its tracks as propulsion. However, this netted a maximum water-going speed of just 4 miles per hour.
Despite the arrival of the modern Mitsubishi Type 89 Infantry Fighting Vehicle, the Type 73 remains in active service in strong numbers with the JGSDF. The Type 89 entered service in 1989 and has reached production numbers of around 70 vehicles - although it should be noted that both vehicles fill different battlefield roles in the Japanese Army.
The JGSDF also makes use of a command vehicle variant based on the Type 73 hull. This model is identified by its raised roof line as well as additional communications equipment carried. The chassis also makes up the automotive component of the Type 74 self-propelled gun (SPG) as well as the Type 75 Multiple Launch Rocket System (MLRS) in service with the JGSDF.