When the Iran was occupied in August 1941 by British and Soviet forces in order to open a save "back-door" for Lend-Lease deliveries to Russia, it happened not to the least in regard of the Iranian State Railway.
The »ISR«, as called briefly, had been built in the late 1930s primarily to connect the Persian Gulf port of Bander-Shahpur with Tehran and the Caspian Sea port Bander-Shah.
There also existed a section leading northwest to the Iranian-Russian border, but this part was not yet fully completed.
After the successful occupation, the British and Soviet forces immediately took over the control of the Railway and launched a regular transport of all sorts of supply goods.
From December 1941 until March 1942, the British War Department sent no less than 155 steam locomotives to the Iran, of which 143 actually arrived and 12 were lost en route.
They were built by North British Locomotive and Beyer Peacock, the first 46 being coal-burners and the remaining 97 oil-burners.
Until the arrival of the US 2-8-2 »Mikado« Steam and ALCo RSD-1 Diesel engines in 1942-43, they carried the main burden of the hauling flatcars, boxcars and tankcars to the Russian zone and remained in service throughout and partially beyond the war.