too short to allow more than two or three beds to be positioned end to end. Britain's Royal Mail commissioned and built the first travelling post office cars in the late 1840s as well. These cars resembled coaches in their short wheelbase and exterior design, but were equipped with nets on the sides of the cars to catch mail bags while the train was in motion. American RPOs, first appearing in the 1860s, also featured equipment to catch mail bags at speed, but the American design more closely resembled a large hook that would catch the mailbag in its crook. When not in use, the hook would swivel down against the side of the car to prevent it from catching obstacles. As locomotive technology progressed in the mid-19th century, trains grew in length and weight. Passenger cars, particularly in America, grew along with them, first getting longer with the addition of a second truck (one at each end), and wider as their suspensions improved. Cars built for European use featured side door compartments, while American car design favored what was called a train coach, a single long cabin with rows of seats, with doors located at the ends of the car. Early American sleeping cars were not compartmented, but by the end of the 19th century they were. The compartments in the later sleepers were accessed from a side hall running the length of the cars, similar to the design of European cars well into the 20th century. Many American passenger trains, particularly the long distance ones, included a car at the end of the train called an observation car. Until about the 1930s, these had an open-air platform at the rear, the "observation platform". These evolved into the closed end car, usually with a rounded end which was still called an "observation car". The interiors of observation cars varied. Many had special chairs and tables. The end platforms of all passenger cars changed around the turn of the 20th century. Older cars had open platforms between cars. Passengers would enter and leave a car through a door at the end of the car which led to a narrow platform. Steps on either side of the platform were used for getting on or off the train, and one might hop from one car platform to another. Later cars had enclosed platforms called vestibules which together with gangway connections allowed passengers