During the decade immediately following World War II, tank cars experienced a dramatic rise in popularity amongst railroads due to gasoline needs of the booming automobile industry. Over this 10 year period, more tank cars were built than ever before or after, and the number of tank cars in service doubled from 50,000 to 100,000. Thousands of these tank cars were ACF Type 21s.
 
First introduced in 1921, the Type 21s remained in use through the 1950s and 60s. Beginning in the 1930s, their brake systems were updated to the safer AB standard. These models represent tanks cars rebuilt with the AB brakes.
 
Models feature nonmagnetic, blackened metal wheels; extremely free-rolling 50-ton Spring Plankless trucks and wheelsets; universal coupler pockets; full underframe detail with Cardwell Draft Gear and AB brake system; and razor sharp printing and graphics.