This set was produced to introduce a more comprehensive set for these classes, which hadn't been done by previous manufacturers.
The FD2, or “Queen Mary” depressed center flatcar was built at Altoona in April 1952 and was the largest freight car in the PRR’s fleet. It had a capacity of 500,000 lbs. and when loaded it weighed over a million pounds. The FW1 was sold to the PRR in September 1960 to utilize the dual bolster trucks of the FD2, but with an open-well body specifically designed for carrying rolling mill housings. It’s capacity mirrored that of the FD2. Both of these cars interchanged trucks with each other throughout their entire service life. These cars, due to their size, lasted in their as-built paint schemes into Penn Central, with the FW1 body being repainted into PC in the mid 1970’s, the FD2 body was repainted from PRR into PC in 1974. Operationally, the clearance diagram for the car was based on which of the two bodies were attached, so even though the car bolsters were numbered for the FD2, the clearance diagram would be for the FW1 or FD2 respectively. The FD2 was retired by Conrail in the 1990’s and currently resides in the equipment collection of the Altoona Railroaders Memorial Museum.
For references in regard to the PRR's FD2 and FW1 Flatcars please consult the Pennsylvania Railroad Technical & Historical Society's publication, Pennsylvania Railroad Flat Cars, Revenue & Work Equipment, 1881-1968, by Al Buchan and Elden Gatwood and Volumes 1-3 of the PRR Color Guide.