The Daylight Speedliner was an American named passenger train of the Baltimore and Ohio Railroad (B&O) in the 1950s and early 1960s.

Equipped with three or four streamlined, self-propelled Budd Rail Diesel Cars (RDCs) coupled together, it initially operated between Philadelphia, Pennsylvania and Pittsburgh, Pennsylvania, via Baltimore, Maryland, and Washington, D. C., as Trains #21–22.

Pleased with their reliability and lower operating costs compared to heavyweight passenger trains drawn by steam locomotives, the B&O decided in 1955 to replace its money-losing Washingtonian steam train with RDCs, ordering four RDC-1s with reclining coach seats and two RDC-2s with baggage compartments.

The RDC-equipped Daylight Speedliner entered service on October 28, 1956, and reduced the railroad's operating expenses by almost half, compared to the Washingtonian train it replaced.

[2] In 1961, the westbound Daylight Speedliner, operating as B&O's Train # 21, departed Baltimore at 9:00 a.m. and then Washington, D.C., at 10:00 a.m., arriving in Pittsburgh at 4:20 p.m. on the following schedule (principal stops shown in blue):[3] Unusual for RDCs, the lead RDC-2 car was configured by B&O as a combination dining car/baggage car/coach (pictured) offering full meal service, with the addition of a kitchen and six tables, listed in B&O's 1961 time table as a "refreshment diner".