[2] During the land reforms of Mohammad Reza Pahlavi in 1963, as part of the "White Revolution", the Trans-Iranian railway was extended to link Tehran to Mashhad, Tabriz and Isfahan.

However, the Russian government declined such proposals, fearing that it would jeopardize Russia's geographically enabled commercial dominance in Iran as well as complicate relations with the British.

Zveginstov, supporters of the Anglo-Russian Entente, promoted a private initiative for a railway connecting India and Europe, to counteract the economic threat Germany posed to the region.

Lord Curzon, British Viceroy of India, rejected the loan, suspicious that the Russians had an acquisitive eye on Britain's precious Indian colony, provoking stark protest from Sazonov against the accusation.

However, Sir Edward Grey, Britain's Secretary of State for Foreign Affairs, refused to force the Iranians to accept Sa'd Dawla as Prime Minister, because of his aversion to the Constitutional movement in Iran.

Fearing the implications of the impending war, Grey at last found it in Britain's best interest to concede at last, and agreed to initiate application of the railway under the Balmoral conditions.

[14] Initially, British and Russian observers considered the implantation of railways as the ultimate solution to the immense transportation problems Iran faced due to sparsely settled population, the lack of rivers, high mountains, and inhospitable desert regions of the country.

Some British critics, including General Percy Sykes, opposed the railway because it ran north to south, rather than from west to east.

The west to east route was preferred because it would allow the British direct access to their military bases in India and Mesopotamia, and at the same time, avoiding the threat of commercial loss of profit to Russia and any foreign rival.

[15] However, if a cabinet minister was caught criticizing the extensive tax burden the railway produced, he could be placed in prison on counts of being a British collaborator, decidedly attempting to keep Iran backwards for his own financial and strategic goals.

[17] The majority of capital used to fund the railway was provided through taxes on goods such as sugar and tea, produced in plants set up by the industries ministry, as part of Reza Shah Pahlavi's reform movement.

[18] In the following years Reza who became Shah in 1925 had legislation passed in parliament which secured internal Iranian funding for the railway project from taxes levied on consumption of sugar and other goods thus excluding a new round of external debts that had bogged down the rulers of Iran before World War I.

From 1927 an international syndicate called "Syndicat du Chemin du Fer en Perse" consisting of the American Ulen and Company and a German "Konsortium für Bauausführungen in Persien" (formed by 3 German companies Philipp Holzmann, Julius Berger and Siemens Bauunion[19]) undertook the construction of the initial test lines.

The German group started from the new harbour of Bandar Shah on the Caspian coast to the foothills of the Alborz mountains at Shahi (Qaem Shahr).

Kampsax at that time was active in railway construction in Turkey and the Shah followed the Turkish recommendation which had the additional advantage of bringing in a company from a small country which posed no political risk for Iranian independence.

The Three Golden Lines (Se Khat Tala) spiral is on the Mazandaran branch in the Sewatcow (Savadkuh) County of Mazanderan just a few kilometers south of Veresk Bridge.

[24] However, Kampsax' contractors laid relatively lightweight rails, ranging from 67 to 75 lbs per yard, that restricted the axle loads that the line could carry.

[25] Various geological problems were encountered, requiring abandonment of some tunnels and realignment of the route through different terrain: In 1936 Beyer, Peacock & Company supplied Iran with four Garratt 4-8-2+2-8-4 articulated locomotives (works numbers 6787–6890).

[26] The British and Russians initially stated their reason for invading Iran was the Iranian government's failure to rid the country of Germans, who supposedly were planning an eventual coup d'etat.

[33] In the same year Davenport Locomotive Works supplied 24 diesel-mechanical 0-4-0 switchers, designated class 20.01,[34] that Iran had ordered before the Allied invasion.

[35][36] In 165 miles (266 km) the line has 144 tunnels, in which smoke and oil fumes created harsh working conditions for steam locomotive crews.

[25] In April 1943 [35] another 18 ALCO RSD-1's entered service,[26] enabling the USATC to return some LMS 2-8-0s to the British Middle East Command[24] and extend diesel operation northwards, reaching Qom by September 1943 and regularly serving Tehran by May 1944.