Russia’s Only Pump-Jet Kilo Class Submarine Is Back To Attack Ukraine

A unique Russian diesel-electric submarine, the Alrosa, has returned to sea for trials ahead of rejoining the Black Sea Fleet with a new armament of cruise missiles. The one-off submarine, the oldest in the Black Sea Fleet, is likely to join combat operations against Ukraine, where Russia is now waging an intensified campaign of missile bombardment.

Russia’s state-owned TASS news agency reported today that the Alrosa, a sub-variant of the Project 877 or Kilo class diesel-electric boats, went to sea to begin post-upgrade trials. This had been disclosed by the Black Sea Fleet’s 13th Ship Repair Plant in Sevastopol, Crimea.

“The submarine has deployed [to the sea from the Sevastopol Bay],” the plant said. “For the first time over eight years, it will be tested in various modes of operation and must prove its ability to operate according to its designation.”

Photos and videos also appeared on social media today, showing the Alrosa leaving the repair facility. It is important to note, however, that it’s unclear how long these trials will take and exactly when the submarine will be declared ready for operational service. Furthermore, these are factory trials that are likely to be followed by further trials carried out by the Russian Navy.

There are few details of the extent of the upgrade, but it’s widely stated to have included the addition of 3M14 Kalibr subsonic cruise missiles, known to NATO as SS-N-30A Sagaris. These weapons have been widely used by Russia since the start of the war in Ukraine, being launched from surface combatants and submarines. Before that, the weapon was employed by the Russian Navy during Moscow’s intervention in the Syrian Civil War. The Kalibr is widely analogous to the RGM-109 Tomahawk and is thought to have a range of between 930 and 1,550 miles, carrying a high-explosive warhead weighing 990 pounds. The Kalibr missiles can also be exchanged for 3M54 anti-ship missiles, but with the absence of a meaningful Ukrainian surface threat, these are unlikely to be carried at the moment.

Last month, reports in the Russian state media described upgrades to the Alrosa that included “new combat and technical capabilities” that brought it up to a standard comparable to the “six subs that had arrived for the Black Sea Fleet in recent years.” This is a reference to the latest Project 636.3 or Improved Kilo class boats that make up the rest of the fleet’s submarine arm and which feature a Kalibr missile capability from the outset. These more modern boats were delivered between 2014 and 2017.

What’s unusual about the Alrosa, which was completed to a unique standard also known as the Project 877V, is its propulsion system. While the standard Kilo class diesel-electric boats are driven by a six- or seven-bladed propeller, the Alrosa has a pump-jet propulsor, technology that you can read about in detail here.

Suffice it to say, a pump-jet offers an array of advantages over propellers, above all the ability to reach higher speeds without noisy cavitation — this means they can transit long distances around much more stealthily. According to Russian accounts, pump-jets boats are nicknamed “black holes” due to their noise-suppressing features.

Moreover, pump-jets are also more efficient across most of a submarine’s performance envelope and have particular advantages in shallow water, as in the Black Sea. At the same time, pump-jets are heavy, costlier, and more complex than a propeller, but they have found recent use on some of the Royal Navy’s Trafalgar class and later the U.S. Navy’s Seawolf class and Virginia class nuclear attack submarines, and many other subsequent classes.

The Alrosa, in drydock, revealing details of its fairly advanced pump-jet design. Uncredited

In the case of the Alrosa, it seems the pump-jet was always intended for experimental use only and it has not reappeared on later iterations of the Kilo design. Pump-jets do, however, drive the Russian Borei class nuclear-powered ballistic missile submarines.

The Alrosa is a significantly older submarine, built at the Krasnoye Sormovo Shipyard in what was then Gorky (now Nizhny Novgorod) and originally launched in September 1989, shortly before the fall of the Soviet Union.

With the demise of the Soviet Navy, the Alrosa was left in Crimea, then still part of the newly independent Ukraine. In 1992, most of the Black Sea Fleet came under Ukrainian control, and attempts were made to establish an independent Ukrainian Navy. Russian reports state that in March of that year Ukraine attempted to seize the boat for its own use although a lack of spare parts and batteries at the time meant the submarine saw only limited operations.

Regardless, the situation quickly led to tensions with Moscow and an agreement for a joint fleet under bilateral command, although in practice this was dominated by the Russian Navy, which retained its foothold in Crimea. The Ukrainian Navy continued to exist, too, as a separate entity.

Finally, in 1997, a treaty was signed that divided assets of the former Soviet Black Sea Fleet between Ukraine and Russia, with Moscow paying Kyiv for the privilege of using Crimean naval facilities under a lease agreement. At this point, the Alrosa became the sole active submarine in the Russian Black Sea Fleet, the strategic importance of which had diminished immediately after the end of the Cold War.

The Project 877V submarine Alrosa at Sevastopol in August 2005. Vyacheslav Argenberg/Wikimedia Commons

With the Russian annexation of the Crimean peninsula in 2014, the Ukrainian Navy was evicted, and the Russian Black Sea Fleet came to control additional former Ukrainian Navy vessels.

In the years since the annexation, the Alrosa has languished in port in Sevastopol. While its upgrade and reactivation began well in advance of the current war in Ukraine, it seems that the decision to return the submarine to the Black Sea Fleet may very well have been driven by the demands of the conflict, and especially the need for cruise missile platforms.

Until earlier this month, it had been expected that the Alrosa would transfer to the Baltic Fleet, once it was back in service, and would then be used as a training submarine for crews destined for the newer Project 636.3 boats. Originally, this transfer was planned for 2020 but was reportedly held up by delays in the repair work.

Then, on June 17 this year, it was announced that, after all, the Alrosa would stay with the Black Sea Fleet, joining the 4th Independent Submarine Brigade in Sevastopol.

The decision to keep the Alrosa in the Black Sea Fleet may well also have been influenced by the availability of the local fleet’s other six submarines. Unconfirmed accounts suggest that, as of mid-June 2022, the fleet had only two submarines fully active and operational in the Black Sea, with another two underway in the Mediterranean. Of the remainder, one was in drydock, one had been last noted underway in May, and another was moored at Sevastopol. With that in mind, what looks like a relatively large force on paper can quickly be reduced by other operational and maintenance requirements.

Even without stepping up the tempo of its cruise missile attacks the current situation leaves the Black Sea Fleet notably short of submarines. The viability of returning the two submarines in the Mediterranean to the Black Sea is also somewhat unclear, due to the terms of the Montreux Convention.

The convention puts restrictions on non-Turkish warships transiting between the Black Sea and the Mediterranean and extends to Russian submarines. An exception can be made if the submarine is moving to or from its Black Sea homeport for repairs, which is an argument that Moscow has used in the past. This has notably been the case for combat operations by Black Sea Fleet submarines in Syria.

However, even with all six of the fleet’s Improved Kilo class boats in the Black Sea, the demands of routine maintenance, crew training, and replenishment of fuel, weapons, and supplies means that the force is under pressure.

Speaking yesterday to his British counterpart Admiral David Radakin, the commander-in-chief of the Ukrainian Armed Forces, Valery Zaluzhny, provided figures for the numbers of cruise missiles launched by Russia against Ukraine. Four days ago, 53 cruise missiles were fired “from various base platforms,” three days ago 26 were fired, two days ago the number was close to 40, and in the previous 24 hours, 12 had been fired.

These missile strikes accounted, among others, for the attack on the shopping center in Kremenchuk in central Ukraine that killed and injured dozens of civilians.

The “various base platforms” include Tu-22M3 bombers launching their missiles over Belarus, as well as Tu-95MS and Tu-160 strategic bombers launching cruise missiles from over Russia. However, naval vessels, including frigates, corvettes, and submarines of the Black Sea Fleet have long played a key role in delivering these strikes.

The Kilo class is relatively compact, and each of the Project 636.3 boats reportedly carries only four Kalibr missiles. Although unconfirmed, it’s likely the updated Alrosa has a similar capacity.

The improved performance offered by the pump-jet propulsion unit is of no consequence in a conflict without any anti-submarine warfare opposition. The fact that the Alrosa had previously been earmarked for a training role suggests that any advantage conferred by the unique propulsor was likely not judged sufficient to keep it in service in a frontline role.

Russian Navy submariners launch Kalibr missiles during naval exercises earlier this year:

Furthermore, the Alrosa has in the past suffered from problems with its powerplant. In 2009, during drills in the Black Sea, the submarine reportedly had an engine malfunction and needed to be towed back to port in Crimea. Not only is the Alrosa an aging boat, but the unique pump-jet propulsion likely poses unique maintenance challenges.

There is also the recurring question of exactly how many advanced cruise missiles Russia has left in its stockpiles. Since early on in the current campaign, there have been estimates that these stocks have become severely depleted, with the effects of sanctions making it even harder to replenish them. This factor, too, is one that has to be taken into account when looking at the numbers of potential launch platforms and what they can actually offer in terms of firepower.

While the Alrosa is unlikely to be a long-term solution to providing additional firepower to the Black Sea Fleet submarine service, the chances of it being involved in the ongoing war against Ukraine are high, especially as the Kremlin embarks on what appears to be a new campaign of extensive cruise missile strikes across the country.

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