The following is claimed in an article, in Swedish and without sources, found here (among other sites):
[demokratbloggen.wordpress.com]

Here follows a short summury of mine in English:

As a part of, or extension to, the Molotov-Ribbentrop agreement, Soviet let the Germans establish a naval base called "Bas Nord" in "Lista fjord" 45 km east of the Soviet Norwegian border. The same place is said to be a major Russian naval base still today (Zapadnaya Litsa).

U38 was the first German warship to enter the site to start establishing the base on 26th November 1939. Other ships mentioned using the base were the weather ship Kedingen, the trawler Sachsen and the whaler Sachsenwald and the (oil) freighter Jan Wellem. The supply ships Venezia, Iller and Viking-5, based in Lista, are said to have supplied u-boats and raiders in the North Atlantic.

This base was allegedly instrumental in making the German invasion of Narvik a success. After the (oil) supply ship Kattegatt from Wilhelmshaven was sunk by the Norwegians, Jan Wellem, from its base on Soviet territory, could refuel destroyers and unload 500 tons of supplies for Wehrmacht troops in Narvik.

What do you know about this base? It must have been of great help for the u-boats until the invasion of Norway made it redundant. The article raises the question that Soviet-German cooperation during the time of the Molotov-Ribbentrop agreement might have been even more extensive in ways still not well researched.