sentences:  A prototype MTB-82m was built in February 1946 at a military factory.Following the construction of 77 additional MTB-82 trolleybuses in 1946–47, improvements in the design led to the introduction of the MTB-82d.Production of the improved model continued at military factories as well as at MTRZ, a small trolleybus repair plant in Moscow, until 1951, when the Uritsky factory was established in Engels to take over all trolleybus production from the various smaller facilities.