Question on the siege of Leningrad

[PanzerMike]

Are the USSR units out of supply or not?

[Journier]

they are not out of supply because leningrad has a port, to supply, you need to blockade the port as well?

aircraft can interdict some? or maybe sometimes all of the port supply if on naval attack. but personally i never find they interdict all port supply.

[AlbertN]

Leningrad is a supply source for Soviet Union as it is a production city.

[PanzerMike]

Okay. And it can supply an unlimited number of units indefinitely?

[AlbertN]

Yes.
Production cities are supply sources for their own nation.