The Persian Corridor was a supply route through Iran into Soviet Azerbaijan by which British aid and American Lend-Lease supplies were transferred to the Soviet Union during World War II. Of the 17.5 million long tons of U.S. Lend-Lease aid provided to the Soviet Union, 7.9 million long tons (45%) were sent through Iran. This supply route originated in the US and UK with ships sailing around the Cape of Good Hope to the Persian Gulf. From there, the materiel transited Iran to the USSR. Other supply routes included the Northern route across the Arctic, and the Pacific Route which handled US cargo at Vladivostok and then used the Trans-Siberian Railway across the USSR. This Persian Route became the only viable, all-weather route to be developed to supply Soviet needs. Etymology English-language official documents from the Persian Corridor period continue to make the word "Persia" interchangeable with the name of Iran. In correspondence by the government of the United Kingdom, usage of "Persia" over "Iran" was chosen by Winston Churchill to avoid possible confusion with neighbouring Iraq. Overthrow of the Shah Following Germany's invasion of the USSR in June 1941, Britain and the Soviet Union became allies. Britain and the USSR saw the newly opened Trans-Iranian Railway as an attractive route to transport supplies from the Persian Gulf to the Soviet Union. Britain and the USSR used concessions extracted in previous interventions to pressure neutral Iran (and, in Britain's case, Iraq) into allowing the use of their territory for military and logistical purposes. Increased tensions with Britain led to pro-German rallies in Tehran. In August 1941, because Reza Shah refused to expel all German nationals and come down clearly on the Allied side, Britain and the USSR invaded Iran, arrested the monarch and sent him into exile to South Africa, taking control of Iran's communications and the coveted railway. In 1942 the United States, now an ally of Britain and the USSR in World War II, sent a military force to Iran to help maintain and operate sections of the railway. The British and Soviet authorities allowed Reza Shah's system of government to collapse, and they limited the constitutional government interfaces. They installed Reza Shah's son, Mohammad Reza Pahlavi onto the Iranian/Persian throne. The new Shah soon signed an agreement pledging full non-military logistical cooperation with the British and Soviets, in exchange for full recognition of his country's independence, and