A few months back I had talked about submarine tankers here, here, here, here, here, here, and here.
I also talked about LNG being shipped to the Baltics by submarine tankers.
In the link you will find the submarine LNG route to the Baltics in a hatched line.
Just recently, a company from Pontiac Michgan visited one of the threads on submarine tankers. I won't say who the company is but, I will say they are involved in carbon trading, oil and gas and naval marine technology...
In the link that is from Russian researchers, you will find a diagram titled:
Submarine Tanker Construction at Sevmash Plant in Severodvinsk
On a thread that was posted on if submarine tankers were in Gazprom's future, I pointed to an article on Russian military secrets showing up on the internet.
However, I added that the classification and size of the submarine would fit that of a submarine/cargo tanker.
In an article in 2007 published by the Kommersant with its headline: Submarine: Military Secret Shows Up on the Internet
On September 6, the official site of the city of Sarov (www.adm.sarov.ru) reported on a visit to the city by the commander of the submarine Sarov Capt. 1st Rank Sergey Kroshkin. In the text, it stated that the Sarov was still in the stocks at the Severodvinsk but “the chief commander of the Navy has set the task of finishing work by the end of the year.” The number of the submarine project was given: 20120 and its technical and tactical characteristics as well. those data indicate that the new submarine is very similar to the Project 877 Paltus (Halibut) diesel submarine, but its water displacement is greater (3950 vs. 3050 tons).
On September 11, that information disappeared from the site, but it had already been reprinted by the local media. Russian Navy press service representative Alexander Smirnov told Kommersant, that he “knows nothing” about the Project 20120. Kommersant contacted the Zvezdochka shipbuilding enterprise and Northern Machine Building Enterprise (Sevmash) in Severodvinsk for commentary about the submarine. A Zvezdochka spokesman stated that no new submarines are being built there. Sevmash declined to answer Kommersant's questions. The Rubin central design bureau, a leading developer of submarines, also declined to confirm or deny its involvement with the Project 20120.
There is no doubt that building of submarine tankers is being seriously looked at by the Russians and may even be in the actual construction process. And I will say given who has visited the threads, it is being looked at here in the U.S.