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The Evolution of the 1937 AAR design boxcar

The first all-steel boxcar was proposed and approved by the American Railroad Association (ARA) in 1932, and had an inside height dimension of 9’-4”, mostly in accommodation to Eastern railroad tunnel restrictions. The Depression delayed the sale of these cars and by the time of the economy’s resurgence and only about 15,000 were ordered in 1936. By 1936, the A.R.A./A.A.R. evolution of the 40’-6” all-steel boxcar design moved to the 10’-0“ IH car, becoming the most common of all A.A.R. standard boxcars: the 50-ton 1937 A.A.R. with 10’-0” inside height (IH). The Car Construction Committee approved this revised design in June 1936 and cars of the type were built from 1936 to 1947. The common version of this car had 10-panel riveted sides with 6’ door openings, 4/5 Dreadnaught Ends, and a Murphy rectangular panel roof. The A.A.R. design was modular in concept. The side panels, ends, and roofs were interchangeable components parts that conformed to A.A.R. standard dimensions. Often car builders such as American Car & Foundry, Pullman-Standard and Pressed Steel Car Co., found it more economical to order roofs, ends and sides from fabricators such as Standard Railway Equipment Co. of Chicago and install them in their shops.

Many variations existed in the selection of ends and roofs used on this family of cars. Early versions built until 1939 typically had square corners and later versions had round corners with W-section corner posts - a stronger design. In 1941, the A.A.R. approved an optional taller design with a 10’-6” inside height, commonly known as the Modified 1937 AAR boxcar. These quickly became the 40’ boxcars of choice by most railroads, particularly those located in the Midwest. However, other roads continued to purchase 40’ boxcars with a 10’-0” inside height during the immediate postwar period and the 1950’s such as the Southern Pacific. This was often due to tunnel or other clearance restrictions. By 1947, over 119,000 of the 1937 AAR 10’-0” IH boxcars were in use throughout the US and Canada, followed by an almost equal number of Modified 1937 AAR boxcars.

As the depression waned, in 1936, the Southern Pacific began a vast program of replacing their aging, large fleet of single-sheathed boxcars, such as the B-50-14 and 15, with the new 1937 AAR all-steel design, designations beginning with Class B-50-18 and 19. Opting to forgo the higher volume of 3,898 cu. ft. of cargo space offered with the Modified 1937 AAR design, the SP stayed with the 10’-0” inside height version with 3,713 cubic feet of loading space. These cars were ordered and received as follows:


B-50-18 - Series 32770-33269, 500 cars, Pullman-Standard Car Co., Lot 5537 - delivered December 1936
B-50-18 - Series 33270-33519, 250 cars, American Car & Foundry, Lot 1535 - delivered October 1936
B-50-18 - Series 33520-34019, 500 cars, Pressed Steel Car Co, - delivered December 1936
B-50-18 - Series 34020-34519, 500 cars, Bethlehem Steel Car Co. Lot 8484 - delivered February 1941
B-50-19 - Series 37840-38089, 250 cars, Pullman-Standard Car Co., Lot 5549 - delivered March 1937
B-50-19 - Series 38090-38339, 250 cars, Pressed Steel Car Co, - delivered September 1937
B-50-19 - Series 38340-38589, 250 cars, American Car & Foundry, Lot 1608 - delivered October 1936
B-50-19 - Series 38590-38839, 250 cars, Bethlehem Steel Car Co. Lot 8745 - delivered February 1938

(In 1956, all these cars were renumbered into 114753-117411 Series to free up numbers for newer cars.)

Boo Rim Precision Scale of Korea, has produced an exquisite and accurate model in all-brass of this S.P.’s series using builder drawings from both the Pullman Library in Illinois and the Museum of Transportation in St. Louis (AC&F) and dozens of 8 x 10 glossy photos of the prototype both as builder’s photos and many in-service photographs.

Accurate decal sets for the 3 time period’s lettering schemes used on these cars are available from Protocraft Decals based on the artwork of Rick Leach, Southern Pacific Mechanical Dept lettering arrangement drawings and numerous photographs.

Although the 10’-0” IH 1937 AAR 850 car project undertaken by Protocraft, has essentially sold out, 9 models of this version were recently discovered in a mislabeled box and are now being placed back in stock. To order on of these outstanding models CLICK HERE


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