Used the sea, used the sea, used the sea.
Leningrad (now again St. Petersburg) sits on the sea coast (the Baltic Sea).
It's backed by the massive great lake 'Ladoga'.
In the War the Nazis (and the Finns) had blocked the city on 3 land sides leaving only the water (or ice) surface of Lake Ladoga open...by land.
But...the seaside remained open throughout and was never used.
The Soviet Union at the time 'did' have a navy almost as good as the German but Stalin never used it...plus...the British had a navy at least 5 times better/ bigger than the German.
It should have been possible to relieve and supply Leningrad by sea with a combined Russian-British fleet. Of course German air power would harry them from Denmark on...but the British could have included aircraft carriers, used neutral Sweden to advantage and counted on the Finns never to fire at the British...The naval run for the British (with Russian help) to Leningrad should have been no worse than the British naval run to Malta done at the same time without any help.
Why wasn't it done?......
1.) Stalin was a true Russian 'land guy' he thought only of land infantry and land tanks...the use of naval and air-power mostly never occurred to him.
2.) Stalin wanted (and said so) the Russian people of Leningrad to be trapped in there and fight like cornered rats to the bitter end.
3.) If they won...Stalin didn't want a British non communist land force in his 2nd most important city.
3.) The British preferred spending British lives and ships to save Britons in Malta than to save Russians in Leningrad.