Bruce Hansen writes: This Half-track was built from a 1949/50 12 1/2 set. The P55 motor drives the half-track forward and backward.
Underside view: the chassis frame is made from a pair of DP 12” angle girders. The P55 motor drives the model along at about 3 inches/second.
This model has a pair of idler pulleys which give the track a taller profile. This helps the model climb forward or reverse over taller obstacles (no problem with golf ball sized rocks).