Short answers, pulled from the story.
The Persian Corridor was a supply route used by the Western Allies to transport material support from the Persian Gulf to the Soviet Union during World War II. It became the only viable all-weather route developed for Soviet needs after other options proved insufficient.
Britain and the Soviet Union invaded Iran in August 1941 to take control of communications and the Trans-Iranian Railway. This invasion occurred after Reza Shah refused to expel German nationals or clearly side with the Allies.
7.9 million long tons of US Lend-Lease aid traveled through the Persian Corridor out of 17.5 million long tons provided to the Soviet Union. This figure represented 45 percent of total American aid sent to Russia excluding transfers of warplanes via Persia.
Colonel Don G. Shingler originally commanded the mission before being replaced late in 1942 by Brigadier General Donald H. Connolly. The unit later renamed itself the Persian Gulf Service Command under the authority of the US Army Forces in the Middle East.
The Persian Corridor became the only viable all-weather route developed for Soviet needs while other routes faced seasonal limitations or enemy threats. It handled more cargo than any other single route despite the existence of Arctic Convoys and the Pacific Route via Vladivostok.