"Rail Movement" or strategic movement of ground forces is not allowed through Arid/Desert terrain - There is no distinction between Arid and Desert - they are the same on the map - the tan territories are Arid/Desert.
So if you start in an Arid/Desert territory you may not rail move. And if you start elsewhere, you must stop in the first arid/Desert territory you enter.
I simlified the political situation of Persia for game play purposes. Eastern and Western Persia are British. Tabris is Soviet. They actually divided Persia up between themselves in 1941 - to simplify things - I just make it part of the Nazi-Soviet Pact.
Britain can move units from Egypt to India via land movement - but since these territories are arid/desert - there is no ral movement - so they would have to marsh tactically - which would take a while.
Russia is supposed to occupy Tabriz any time they want - as long is it is not Axis occupied, the Allies can lend lease production points there (at a rate of 4 for 3 I believe). The allies can only begin to Lend Lease Russia once Russia is at war.
Does this clear these rules up for you?
cheers,
Mark