After entering the First World War, the Russian Empire urgently needed heavy freight locomotives in order to be able to transport war supplies over mountainous sections. The aim was to replace the outdated Series Ф (F) Fairlie locomotives. It was planned to order a single-frame locomotive with five coupled axles. Since there was no way at that time to produce large numbers in Russia in a short time, the locomotives were ordered in North America.
20 years earlier Baldwin had delivered two four-cylinder compound locomotives in 2-10-0 wheel arrangement to the Transcaucasian Railway, which were known as the ДK (D-K) series. Now there was the opportunity to purchase 400 locomotives from North American manufacturers in a short time. 250 came from Baldwin, 100 from ALCO and 50 from the CLC. The designs originated in Russia and were adapted to imperial dimensions in America for ease of production. The grate area was set at six square meters in order to be able to burn coal of a lower quality. The first 400 locomotives from the three manufacturers were named EФ for Philadelphia (Baldwin), Ec for Schenectady (ALCO) or Ek for Kingston (CLC).
A further batch with minor improvements was designated EЛ in honor of Lomonosov. When the USA entered the war, it was possible to produce larger quantities as war aid. In total, depending on the source, about 881 pieces were delivered to the Russian Empire, some of which were lost on the long sea route from New York to the Far East. About 200 pieces were distributed to customers in the USA because they could not be delivered after the October 1917 revolution.
Although the engines were a successful design, they initially showed some deficits in operation. These were in part due to corrosion during sea transport, which led to problems with the firebox and other assemblies. Likewise, people in Russia were not yet familiar with the maintenance of the bar frames that are common in North America and therefore initially had to contend with high failure rates. Gradually, however, one could become friends with the machines and found ways to maintain them sufficiently. Thus, later larger numbers of the series Е of the Soviet railways were built.