Compare the Submerged Displacements and See What Fits

Submarine Alrosa disappeared in a news blackout since an event decribed as minor. Russian military officials described the sub’s problem as minor, but added that the vessel could not make it to its home port, Sevastopol, on Ukraine’s Crimean Peninsula. It was towed to the nearer port of Novorossiysk on November 23, according to the RIA Novosti news agency. The Alrosa is a Project 877 Kilo class submarine. Multiple accounts of Alrosa's recent misadventure are disputed by various sources within and without Russia. As yet, no Russian admiral has offered an official press release.

Alrosa's submerged displacement is given here and elsewhere as 3950 tons. Keep that in mind when reading the excerpt below an earlier article about a hybrid diesel sub with an RTG power pack:

Sep. 12, 2007 - Kommersant. Publishing House - Submarine: Military Secret Shows Up on the Internet [ed. B-90 Sarov Project 20120 [1] ]

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).

Both The Sub Report and Galrahn of Information Dissemination noted the interesting Sarov story.

Are Sarov's and Alrosa's displacements actually different? Contrary to what Kommersant tells us above, there appears to be no difference at all in Alrosa's and Sarov's submerged displacements (3950 tons). Why is this important? Is someone trying to mislead us?

Suppose the last operational Russian sub in the Black Sea (the Alrosa) is being refitted with her own RTG (backup energy source) and, therefore, the capability to spend longer periods under water? Would it not be much easier to make the similar-looking Sarov, assuming her sea tests have now been successful, appear to be the Alrosa and send it to Black Sea ops? Here is another thought from someone else.

Submarines are always silent and strange.