The Lionel Baltimore & Ohio Budd Unit No. 404 was available in 1957 and 1958. This motorized baggage/mail diesel would be painted SILVER with BLUE heat-stamped lettering and "BUDD RDC-4" adhesive nameplates. There was an ornamental horn at each end that has power unit trucks with operating magnetic couplers. Lighted by three lamps that showed off the silhouetted window strips and lighted both headlights, this engine came with two axle Magnetraction, and a three position directional unit that controlled the single vertical worm drive motor, and an on board horn that used a battery. There are no variations.

All of the Lionel Budd units are designed to work on the tighter radius of O27 gauge track, but they will run equally well on O gauge track.