In World War II, the USATC designed a 0-6-0T switcher for use on standard-gauge tracks in Europe and Africa. The S100 was a typical American design with bar frames, outside cylinders and outside Walschaerts valve gear and had a fully closed cab. Between 1942 and 1944, a total of 382 were built by three manufacturers from Pennsylvania and Iowa. They were delivered to the British War Department and stored until D-Day.

After the war, they found new operators around the world. The biggest user was the French SNCF with 77 which were designated 030TU. The Southern Railway in the UK bought 15 and used them around the Southampton docks. They were only operational in 1947 since they received many modifications for use in this country. These locomotives, which were called the USA class, were only withdrawn in 1967. In Yugoslavia, the S100 was designated class 62 and Đuro Đaković even built more which were nearly identical, but had plate frames. Some were still in commercial service after the turn of the millennium.

The Austrian ÖBB used ten as class 989, China Railway had 20 which were designated XK2, the Greek Railways called their 20 locomotives Δα and the Italian State Railway used four as class 831. Additionally, many were used by industrial operators in the USA, UK and Netherlands. Even more operators were located in Egypt, Iran, Iraq, Israel and Palestine. It is not surprising that many are still surviving in several countries with some still being operational.