Re. Soviet equivalent, Alexey Sokolov mentions a so-called "Skorpion" project in the early 60s to launch D-9 SLBMs from converted arctic cargo ships from Project 505. The intention is clearly mentioned to camouflage these ships as civilian shipping or auxiliary vessels. Two designs were studies, as Projects 909 and 1111.
Naturally, none left the drawing board. After the first Polaris SSBNs entered USN service, the D-9 missiles found their way onto the Project 667B (Delta-1) conventional SSBNs and the complete Skorpioncproject would be considered redundant.
More info on the project (in Russian) here.
Also in another style, remember that the Italian Navy was well on its way to refit the pre-war cruiser Guiseppe Garibaldi with Polaris missiles, before their whole nuclear deterrence went south.
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Soviet Century/Cold War 2020 Alternate Universe: Soviet and other Cold War designs 1990-2020.
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