Question:
Does a turn out of supply in SF consists of two player turns?

Answer:
A turn out of supply in SF is one game turn, consisting of an Axis player turn followed by an Allied player turn.

Example: An Italian unit is put out of supply during the Jul I 43 Allied player turn. When supply is checked during the initial phase of the Axis Jul II turn, that Italian unit is noted as being out of supply and gets a U-1 marker (I use red for Axis turns).

During the Allied Jul II player turn the unit remains out of supply.

The Italian unit has now spent one turn out of supply (Axis and Allied player turns). If, during the Axis Initial phase of Aug 1, the Italian unit is still unsupplied at that time, it will be marked with a U-2 marker and is affected by all effects of being U-2’d from that instant on, until it is no longer unsupplied, is eliminated or (during the Axis Aug II initial phase) is marked with a U-3 marker for remaining out of supply.

Source:
TEM 59/60