German Sd.Kfz. 251s were studied as potential references for the upcoming pre-production design. Concept work on the new APC began at the Zavod imeni Stalina (ZIS) factory in Moscow, overseen by Soviet engineer Boris Mikhailovich Fitterman, at roughly the same time the Izdeliye 141 was being developed by GAZ. Prototypes were built with automotive components from the ZIS-151 production line; however, the APC chassis incorporated a more powerful engine and a shorter wheelbase than its utility truck counterpart. Design work was carried out by a team of five ZIS employees: Fitterman, K. M. Androsov, A. P. Petrenko, V. F. Rodionov and P. P. Chernyaev. The final prototype was trialed by the Soviet Armed Forces in December 1949 and accepted into service as the BTR-152. Serial production of the BTR-152 under the manufacturer's code ZIS-152 commenced around mid 1950, making it the first mass-produced Soviet APC. Despite being designed around the same time, the BTR-40 did not enter serial production until the end of the year. The BTR-152 was used by the Soviet military as a command and communications vehicle, fire support vehicle, artillery tractor, and general transporter. Being open-topped, the BTR-152's crew was vulnerable to indirect fire. In later years, the vehicle was not ideal for the prospect of a major conventional war in Europe either, as it lacked amphibious capability or NBC countermeasures. However, these early BTRs remained effective as a low-cost option that allowed the Soviets to rapidly motorize their existing infantry divisions. A program in the late 1950s looked at ways to replace the BTR-152 with a more sophisticated APC utilizing a purpose-designed, amphibious chassis. As the BTR-152's six-wheeled configuration was deemed insufficient to reduce ground pressure on the tires and produce optimal cross-country performance, Soviet engineers embarked on an eight-wheeled APC program, which resulted in the BTR-60. Approximately 8,600 BTR-152s of all variants were manufactured in the Soviet Union, with some unlicensed copies being produced in the People's Republic of China as the Type 56. Soviet BTR-152s were produced between 1950 and 1959, being supplemented by the BTR-60 from 1960 onwards. As they became increasingly obsolescent, many were shipped to Soviet client states in Africa and the Middle East; the largest quantity of second-hand BTR-152s were accepted by Arab nations such as Libya, Iraq, Syria, and Egypt. Small quantities were also converted to armored ambulances and combat engineering vehicles for the Soviet Army; these remained in