The first all-metal door to gain general acceptance was launched in 1910 by the Chicago Railway Equipment Corporation (Creco), a major supplier of other accoutrements to car builders. Creco three-panel steel doors were used on Pennsylvania Railroad’s X23 boxcars built in 1912 but acceptance of Creco doors remained limited. Things changed in 1923 when the three-panel bottom-supported Creco doors was applied to many PRR X29 boxcars. Variations of the Creco door continued in use into the 1940s.
The Camel Sales Company, which handled the marketing of Youngstown steel doors, introduced a new sliding door about 1925 that would, in time, become the most popular door of the steam era. The three equal-sized steel panels with multiple horizontal corrugations made the Youngstown door easy to identify.
In 1945 the Superior Car Door Company introduced the Superior Welded Car Door for box and automobile cars. Advertising literature explained how the door was fabricated with overlapping panels that were welded in place. Five to seven flat panels were used with wider doors generally having more panels. Superior doors were bottom-supported with the door riding on four ball bearings contained in a carriage along the bottom of the door. Promotional material claimed Superior doors rolled freely and were lighter than the more popular Youngstown doors. Some PS-1 boxcars built by Pullman-Standard in 1954 had six-panel Superior doors.