The Umbau-Wagen or Umbauwagen was a type of German railway passenger coach operated by the Deutsche Bundesbahn (DB) which appeared in the mid-1950s.

After the Second World War, the DB, like the Deutsche Reichsbahn (DR) in East Germany, had a serious deficit of stock as well as a very aged fleet of coaches, a situation which lasted into the 1960s.

In the 1950s the bulk of the fleet for local and Eilzug (semi-fast) trains was still made up of 22,345 four-, six- and eight-wheeled compartment and open coaches of the former Prussian and Bavarian classes from the period before and after the First World War.

The levels of steel production and that of other raw materials of the newly formed Federal Republic did not permit a full replacement of the fleet in those days.

Like the DR in the 1960s the DB was forced as early as 1953 to carry out a modernisation of pre-war coaches - plainly and simply called an Umbau or rebuild.

In January 1954 the coach went into full production at the shops in Hanover, Karlsruhe and Limburg an der Lahn.

From these wooden-bodied compartment coaches only the underbody (which was rebuilt to a common length of 13 metres), the running gear and the brake system was used.

The electrical system on the 3yg(e) coaches only permitted close-coupled pairs to be formed, albeit any combination was allowed apart from BD3yg + BD3yg.

Numerous coaches were also equipped with a control cable for use in push-pull trains; this was indicated by adding the secondary suffix "b" (AB3ygeb etc.).

Not until the middle of the 1980s were the last coaches, which served commuter traffic at the BASF factory in Ludwigshafen am Rhein, taken out of service.

Following the success of the six-wheeled Umbauwagen, the DB intended that the large numbers of eight-wheeled compartment coaches from the early Länderbahn fleets which were still available, should be converted on the same principles.

The last coaches were retired in the early 1990s, because it was no longer worth while converting the doors to automatic locking.

The coaches experienced one final highlight during the Wende, the period after the Berlin Wall came down in 1989/90, when they were used in a large number of extra express trains.

Some of the 3yge coaches were painted in red, the DB's standard colour for traction units, as trailer cars for ET 85 multiples and designated as EB 85 and 885.

Some 4yg coaches were redesignated as Class EB 65 and 865 as trailers in Stuttgart suburban services coupled with ET 65 and 465 multiples.