The Russians haven’t had a secret ship program in years, so this is interesting:

Submarine: Military Secret Shows Up on the Internet – Kommersant Moscow

Municipal authorities in Sarov, Nizhny Novgorod Region, accidentally revealed the design for the latest Russian submarine when it posted an account of a meeting with its commander on its website. The high level of secrecy surrounding the submarine suggests that it is a unique experiment on the part of scientists and the military.

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).

The article further goes on to surmise that this submarine has a mini-nuclear reactor on board, so that it can function much in the same way as some of the new conventional boats out there that can stay under water for over a month.

It makes sense. While one could not deploy any great distance with a 500-1000 kw reactor, your time underwater once on station wound be nearly limitless (by comparison, the Seawolf is somethere in the 50,000 kw MW range and has a top speed of over 35 kts).