In 1944 Baldwin Locomotive Works built 20 massive 2-8-8-4 "Yellowstone type" engines for the Baltimore & Ohio Railroad (B&O) and another 10 in 1945, making a total of 30 engines, the B&O's EM-1 class, some of the last steam giants, a class that could rival the Union Pacific's Big Boys; weighing in at 1,010,700 pounds and spanning 83 ft 2.9 in in length. The need for such a locomotive to be built was the outbreak of World War 2; the war caused a surge in rail traffic all over the U.S. and railroads needed bigger and stronger engines to keep up with demand. The B&O wanted to use diesel power but the War Production Board regulated the production of steam and diesel locomotives until the war emergency was over. The EM-1 produced 115,000 pounds-force of tractive effort on 64-inch drivers with 235 pounds per square inch steam pressure and four 24-by-32-inch cylinders. The tender carried 22,000 US gallons of water and 25 tons of coal. Nothing bigger could operate within the tunnel clearances and track restrictions on the B&O's main line. They pulled heavy freight trains for the B&O, as well as the occasional mail and passenger trains, until 1957 where most of them were retired and scrapped, the last run of a EM-1 was on April 19, 1960. But one locomotive, No. 659, almost made it to preservation. The B&O Railroad Museum in Baltimore selected this locomotive as one of their future museum exhibits. However, there was a mix-up in communication, regarding the locomotive’s status, the salvage crew scrapped No. 659, where it stood. Now, none of the EM-1's survive.
